Sorry, can't help in detail, I have not actually had the issue on D2, only the same issue on C4 and C5. I think there are 2 or 3 accessible from inside and one from outside on D2 but I don't know which is which. I think I have seen a post about replacing them somewhere, IT kind of sits at the back of my mingd replaced at least 1 in the past and had a post here or maybe there was something about it on audipages.
Edit
Here is IT's post:
http://forum.a8parts.co.uk/showthread.php?t=1624 but that looks like a different motor. After quick look on internet looks like thee are at least 8 flap motors on D2. V111 would be right center vent motor. If you go in output tests on VCDS you should be able to cycle through all the motors and it should show on screen which one it is activating, then it's a matter of listening where is the sound coming from when V111 is activated
Edit 2
Here are some pdf's from ElsaWin. Also after you do output tests and move flaps from end to end it might clear debri and work OK for a while.