My T-reg V40 was registered in 1999 and, just recently, there is a clacking noise coming from behind the dashboard, in the vicinity of the glove box. My wife likens it to a woodpecker. It starts as soon as I turn the ignition key, and the only way to silence it is to press the air intake button to the left of the Air Con button. A little orange light comes on to warn me that there is no fresh air coming in, but at least I have peace and quiet until the windscreen begins to fog up, whence I have to press the air intake button again and release the woodpecker! I've been advised by a friend who fixes cars that the flap on the air intake is stuck and the only way to free it is to strip out the dashboard to gain access to it. I'm reluctant to do this and I'm contemplating pulling out the air intake switch itself to disconnect its power supply. Before doing so, I'd apreciate any comments or advice. Thank you. Mike

 

I wonder if some of the vent control linkage is jammed. You may be able to inspect by removing the carpeted side panels of the center console. I had something similar happen when I installed an aftermarket stereo and was not careful how I routed the wires.
Stan

 

Many thanks! I'll have a look . . .