It's hard to say with certainty. It might be worthwhile to take a quick video, moving the camera around a bit to help us localize the source of the sound.
Even if you're not running the AC, the car needs to keep the batteries and motors from getting too hot. It's probably the drivetrain cooling system running. As you know, the car is rarely truly "turned off", and will do things like this whenever it feels it's required.
Even if you're not running the AC, the car needs to keep the batteries and motors from getting too hot. It's probably the drivetrain cooling system running. As you know, the car is rarely truly "turned off", and will do things like this whenever it feels it's required.