I have a 2002 A3. Sometimes(randomly) the recirculation flap starts opening and closing continuously when I have my HVAC set on Auto. If I press the "Recirculation" button then the flap stays shut. Using VCDS I found no error in the system. I had a spare HVAC control unit that I tried and nothing changed. Anyone experienced something similar? Any ideas of what the culprit could be? A bad flap motor?