I was taking the trash out late this evening. as I was pasing my Prius I heard a sound of a motor running? Not the motor but comming from under the car say the rear seat area, it sounded like a fuel pump running? The car has been parked for hours. What the heck is going on? I got in and all was off. I started it and then turned it off. Walked to the rear and all was quiet. I don't get it. Can anyone tell me what was going on? I am getting used to all the vaccuum releases that go off moments after shut down. But this is hours and way disturbing.... HELP PLEASE.