The HVAC system has a number of small servos, all worm driven with tiny motors that are used to open/close all number of flaps to make air go (or not go) where you want.
There is a common problem on the facelift cars where one of the flap motors fails and either sits there endlessly buzzing, clicking, whiring or generally carrying on when it doesnt need to. If you've got odd repetitive noises coming from behind the dash, this could be your problem.
Interestingly, in every case I've seen its always been the same flap motor, this one:
You dont need the glovebox out to get to it, I just happened to have mine out still. You just need the transmission tunnel cover off, which is 1 screw and some cautious manouvering....
The motor is held in by 2 small cross head screws and comes straight off very easily. If you're uncertain if it is the item making noise, unplug the yellow connector on it and see if the noise stops first. Simple as that....
I've just changed one on mine as it was really annoying and inexcusable not to fit it whilst the car was in bits
