I'm still getting used to my "new" 03 A6 3.0Q and don't recognize all the noises. Is it normal for the car to make a quiet whining noise when you shut off the engine? It almost sounds like a fan/turbo whine when I turn it off.

 

My 2000 A6 2.8 Q will do the same thing - It seems to have something to do with the coolant system. I noticed when the cart is initially turned off there is a motor running and then I noticed there was fluid being pumped in to the overflow tank and that fluid stopped when the "motor" or whirring sound stopped. I assume this is normal but I have never actually looked in to it. I don't think the 3.0 has a turbo but if it has a turbo they can take some time to spin down. I have had turbo cars in the past that recommended running the engine for a minute after stopping the car so the turbo can spin down and not damage the bearings.

 

my friends TL does that too, the coolant system runs for a bit, its factory planned, dont worry