Hello, I am new to the board, and just started having a problem with my 2003 Volvo S40. Last week while running the A/C I began hearing a tapping noise that lasted about 10 seconds, quiet, 10 seconds of tapping, quiet (few minutes). I have taken the fan off below the dash, and while looking up into the vent system and manipulating the A/C controls. I have found that when the system is set to recirculate air, and block vents from outside-> The tapping begins. It appears to coincide with the closure of the "barriers" that swing down to block off different air ducts. You must excuse my lack of auto terminology in explaining this situation. I have made a video of the "barriers" and the noise, video shot from underneath dash looking through area where fan was attached. http://www.youtube.com/watch?v=Kzfxct_N3Oc

Any help would be greatly appreciated. I am just trying to figure out what is causing the noise, and what part/s I would need to fix it.