Minor thing but might as well try to find the answer. When I open my driver's door, car not locked, there is a whirring noise for 1 second. Seems to come from the middle or rear of the car. It's not the seat moving. It may only be after the car sits a while, in the garage. Any ideas?

 

I get the same noise, after parking. I assumed it's the trunk unlocking, since opening the driver's door releases the auto locking system.

 

It does sound like the trunk motor.
The auto locking is something else I don't understand. The car is not locked when it makes the noise (mirrors are not folded). I don't have the key fob on me. And is the trunk really locked if you can open it with the button on the deck lid, without a key? I guess it could still be the trunk, even though it is not really locked in the conventional sense.