[c0nsumer]

Because it was designed with Toyota I don't know if the BRZ does it, but a number of other Subarus will kick on an recovery pump ~6 hours after ignition. It sounds sort of like a small/quiet compressor.

Before I looked up what it was, I kept hearing a gentle noise coming from the garage in the late evening. Figured it was noise from outside... Then one day I was out there and heard it start, realized it was the car, and looked it up.

[rootusrootus]

That is the evap leak testing pump. It pressurizes the tank briefly to test the effectiveness of the cap.

[twisteriffic]

This confused the hell out of me the first time I heard it. Taking the garbage out in the middle of the night and hear whirring coming from under a vehicle that hasn't moved in hours.