My 2005 A6 recently started making noise after I've shut it off. To be specific, I shut the engine off, exit the car, then as soon as I lock the doors, there is a noise that sounds like a pump or a running motor, coming from the passenger rear axle? This noise continues for about 30 seconds to 1 minute after the car and MMI are off, and only does this if the car is locked. Also, if I engage the parking brake, the noise stops. Anyone have any ideas?

 

Did you ever find out what the problem was mine is doing the same thing