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?