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Discussion Starter #1
I walked into the garage this evening and was surprised to hear a humming sound that seemed to be coming from my car. It seemed rather strange that it would be doing that, because the car had been parked for almost 24 hours. It was not plugged in, air temp peaked around 63 F today, so I kind of doubt that it was a cooling fan. The sound reminded me more of an electric fuel pump sound rather than an electric fan kind of sound, but it seemed a bit louder than the fuel pump sounds I've heard in other cars. I walked around the car to convince myself that the sound was really coming from the car and not from some point outside the garage: I'm convinced that it was, but I couldn't confidently reach a conclusion about which part of the car it was coming from. After about 15 seconds, I opened the rear hatch and about three seconds after that, the sound stopped. Anyone have any ideas?
 

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I walked into the garage this evening and was surprised to hear a humming sound that seemed to be coming from my car. It seemed rather strange that it would be doing that, because the car had been parked for almost 24 hours. It was not plugged in, air temp peaked around 63 F today, so I kind of doubt that it was a cooling fan. The sound reminded me more of an electric fuel pump sound rather than an electric fan kind of sound, but it seemed a bit louder than the fuel pump sounds I've heard in other cars. I walked around the car to convince myself that the sound was really coming from the car and not from some point outside the garage: I'm convinced that it was, but I couldn't confidently reach a conclusion about which part of the car it was coming from. After about 15 seconds, I opened the rear hatch and about three seconds after that, the sound stopped. Anyone have any ideas?
My guess is the car was recharging the 12V battery from the traction battery. I've seen a dashboard message about that once or twice. The noise is probably the DC-DC converter used to switch the 360V from the traction battery down to the ~14V needed to charge the little battery.
 
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I get that message about three times a week. Up until now, I've assumed it might have something to do with the fact that my alarm goes off by accident when my key fob bumps up against something in my pocket. And then it usually takes about 30 seconds for me to pull the key fob out of my pocket and shut down the horn. But whatever was humming last night sounded sounded to me like it probably sucked down more power than the horn.


You might be right about it being the converter: that message did light up the first time I drove the car after hearing this sound. But I wasn't aware that the converter would sound like a fuel pump.
 

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I heard it again tonight, under different conditions, and it's kind of disconcerting.


I went out for lunch earlier today, came back around 2 PM and parked in the garage. My EV range was down to about 10 miles. Around 6 PM, I went back to the garage and plugged in the L1 charger. There were a few of the usual clicking sounds as I plugged it in, and then a humming sound started and didn't stop. It reminded me of a fuel pump sound. It was probably about 80F in the garage and it occurred to me that it might be a battery cooling fan, so I opened the rear hatch, lifted the access panel so that I was looking at the traction battery housing, but the sound didn't seem to be coming from there. When I got down on the floor and listened from under the rear bumper, it was pretty clearly coming from somewhere under the car. I'm pretty much convinced that it was a fuel pump sound.


After a few minutes of this, I unplugged the charger from the wall, and then from the car. A moment later, the humming stopped. I reconnected the charger and the humming didn't start again.


I think it's probably been about three weeks since I last drove in a way that required the ICE to start, and I wonder if that might be a factor. It has occurred to me that it might not be good to run the ICE that infrequently. Still, if it really was a fuel pump that I heard, I'm having a hard time imagining how plugging in the charger could have triggered it to come on.


Interested to hear any ideas that people might have.
 

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I heard it again tonight, under different conditions, and it's kind of disconcerting.


I went out for lunch earlier today, came back around 2 PM and parked in the garage. My EV range was down to about 10 miles. Around 6 PM, I went back to the garage and plugged in the L1 charger. There were a few of the usual clicking sounds as I plugged it in, and then a humming sound started and didn't stop. It reminded me of a fuel pump sound. It was probably about 80F in the garage and it occurred to me that it might be a battery cooling fan, so I opened the rear hatch, lifted the access panel so that I was looking at the traction battery housing, but the sound didn't seem to be coming from there. When I got down on the floor and listened from under the rear bumper, it was pretty clearly coming from somewhere under the car. I'm pretty much convinced that it was a fuel pump sound.


After a few minutes of this, I unplugged the charger from the wall, and then from the car. A moment later, the humming stopped. I reconnected the charger and the humming didn't start again.


I think it's probably been about three weeks since I last drove in a way that required the ICE to start, and I wonder if that might be a factor. It has occurred to me that it might not be good to run the ICE that infrequently. Still, if it really was a fuel pump that I heard, I'm having a hard time imagining how plugging in the charger could have triggered it to come on.


Interested to hear any ideas that people might have.
I've definitely head a hum from the rear of the car when charging. My assumption was the same as yours, a cooling fan for the battery. I doubt it's the fuel pump, if the car is off, so is the ECU so it shouldn't be able to turn it on. There is a vent for the battery in the passenger cabin in the foot well of the driver's side rear seat. I assume there is a corresponding exit vent somewhere under the car and a fan to draw air through the battery. That could be the source of the sound we're hearing. :confused:
 

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There are definitely electronics that are powered at all times and extra ones during charging for the BMS. The key fob would not work otherwise. Humming could be coming from the two cooling fans in the PHEV during charging, but also from the inverter.
 

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There are definitely electronics that are powered at all times and extra ones during charging for the BMS. The key fob would not work otherwise. Humming could be coming from the two cooling fans in the PHEV during charging, but also from the inverter.
I agree that there are a lot of things powered on during charging and that many of those can be noisy but the ECU that controls the ICE shouldn't be one of them, that's the one that would run the fuel pump. That should eliminate the pump as the source of the noise deltasmith is asking about.

The noise we referring to is a specific one that only happens sometimes when charging. It's definitely localized to the rear of the vehicle, and sounds very much like a pump or fan. Do you know if there is a dedicated battery cooling fan on the PHEV? The presence of the vent in the cabin implies that there might be and that might be the sound we're hearing during charging.
 

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After my HEV is parked overnight, simply opening the door causes a noise coming from the engine compartment that sounds just like a fuel pump. This sound has been noted a lot on forums, but as far as I know, no one has identified the source.

One ECU does not cover all functions anymore. I think I heard someone say 17 chips in the Niro/Ioniq.
 

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Discussion Starter #9
After my HEV is parked overnight, simply opening the door causes a noise coming from the engine compartment that sounds just like a fuel pump. This sound has been noted a lot on forums, but as far as I know, no one has identified the source.

One ECU does not cover all functions anymore. I think I heard someone say 17 chips in the Niro/Ioniq.
I think I'm familiar with that sound, but it's different from the one I mentioned previously.

The Niro has an amazing abundance of sounds, not all of which are predictable. There is definitely a ghost in the machine. Sometimes I walk out to the car and open the door to put something inside, with no plan to actually drive the car, but as I open the door, I hear a brief hum from under the hood, as if it's anticipating that I'm about to drive. That sound only lasts for about two seconds. There are other times when I do the exact same thing and there is no hum sound.

Yes, there is a fan that is mounted on the PHEV's battery for cooling purposes, although I've never yet heard it run. But you can see the duct work for it and you can see a description of it in the online tech manual.

The sound I mentioned most recently endured for approximately two minutes and probably would have run for longer if I hadn't intervened, didn't seem to be coming from inside the car where I would have expected the battery cooling fan sound to come from, did seem to be coming from under the car, as if from a fuel-tank mounted fuel pump. I probably should have tried to make a video with audio - maybe I'll do that if it happens again.
 

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I believe the PHEV has two battery cooling fans, one under the rear seat, and another under the load floor in back.
 

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Discussion Starter #11
A few days ago, I experienced this for the third time. On this occasion, I managed to record the sound. This forum won't allow me to upload an mp3 file, so I'll share it from google Drive at this URL: NiroHumming.mp3

If anyone has an opinion on whether that's the sound of a fuel pump or a battery cooling fan, I'd love to hear it. I think it's a fuel pump, which leads to the question: why is the fuel pump running hours after the car was shut off?

I had placed my phone on the garage floor, just inside of the rear tire on the driver's side to record this. The car had been parked for at least three hours, the garage temp was approximately 75F, I had driven earlier in the day on all electric but had not run the ICE in at least a few days. The PHEV charger was not plugged in, electric range was approximately 50% when I parked. I'm still thinking this is a fuel pump sound, but I can't rule out battery cooling fan. I did check the battery compartment and could hardly hear the sound in there. I wish I had thought to open the rear door on the driver's side and listen at the vent below the rear seat, but that didn't occur to me at that moment. The sound ran for at least six minutes after I became aware of it; I don't know how long it might have been running before I noticed it.

This may or may not tie in with the fact that I now see Battery Saver+ alerts almost every time I take the car out.
 

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If the noise happens while the battery saver is activated, you may be hearing transformer noise.
 

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I think I'm familiar with that sound, but it's different from the one I mentioned previously.

The Niro has an amazing abundance of sounds, not all of which are predictable. There is definitely a ghost in the machine. Sometimes I walk out to the car and open the door to put something inside, with no plan to actually drive the car, but as I open the door, I hear a brief hum from under the hood, as if it's anticipating that I'm about to drive. That sound only lasts for about two seconds. There are other times when I do the exact same thing and there is no hum sound.
I believe that sound is the brake system applying an initial pressurization (or maybe creating vacuum in the power brake cylinder). Someone on here mentioned that it is pressurized since you must press the brake pedal to "start" the car, and it give a more natural feel to the pedal. I can't say if that is really true (or at least the reason given), but the brake pedal does feel different than previous cars I've owned before the engine starts.
 

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Discussion Starter #15
I believe that the brake pump motor is a different sound. I typically hear the brake pump motor when I open the door while the car is parked, and it typically sounds like it's coming from under the hood, not the rear of the car. If I recall correctly, I can trigger it to run again by pumping the brakes without starting the car.
 

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I'm not staking a lot on my idea, but transformer noise can be difficult to notice. I'm rather sensitive to electrical noise of various sorts and one noise I kept hearing in my house was rather difficult to locate. Turned out to be the power meter on an outside wall. And those are very quiet.
 

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Discussion Starter #17
I think I know what you are talking about. When I was in college, my physics prof ran a tone generator and he kept turning the pitch up higher and higher. He asked the class to put there hand up if they heard the sound, and then put it down when they could no longer hear it (because the pitch was so high). I was one of the last three to put my hand down. I also used to work on a research boat and when we were in shallow water, I could tell because I could hear the sonar pings echoing off the hull, but none of my colleagues seemed to hear that. They looked at me like I was some kind of magician when I told them we needed to pull the nets because we were in shallow water, then they checked the sonar and it was "all hands on deck, now!"

My hearing today probably isn't as good as it was back then, but I'm pretty confident that it's still reasonably good, and pretty confident that I pinpointed the approximate location as being loudest under the car near the rear axles. That suggests to me that it's either the low pressure electric fuel pump, or the battery cooling fan. It occurred to me that I might try to run a test where I back the car out of the garage, park it, put it in Hybrid mode (so that the ICE will start and run for at least a few seconds to warm up), and try to record the sound again, to see if it's the fuel pump or not. My assumption is that the fuel pump would run immediately in that scenario, but the battery cooling fan would not. Not 100% certain this will work, but I think it might.
 

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There are some poor souls (young) who have to return their BEVs because the inverter noise is just too obnoxious to them. Where most cannot hear it at all, including mechanics at dealerships. I've read accounts where the youngest persons at a dealership have to come to the car and not even all of those can confirm the noise.

But there is one more big factor, the brain. The ability to hear a noise is not the same as being bothered by it. While my hearing is probably incredible for my age, all sorts of environmental noise bugs me. However, I have a low level of tinnitus (maybe not officially, but I can hear some low level of white noise - perhaps the base vibration of my inner ear hairs), and I just don't let it bother me. I'm annoyed by it when I focus consciously on it, but then I just let it go.
 

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I think what you are hearing is perfectly normal. I remember being surprised to hear a humming coming from our PHEV when it was parked in the garage at night. I don't believe it was charging at the time, but the sound was coming from under the left rear of the car. I've heard it a few times now, and it seems to only last a few minutes. I assume it's either the battery cooling fan or battery saver operations.
 
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