What Greig said 95%. Turns your fans off and on, change the fan blower mode between body, feet, demister etc. See if any of those cause or stop the clicking.
Mine used to do it but somehow stopped on it own after a year of owning the car.
But I said 95%, because a few months ago I got an (inconsistent) clicking from behind the passenger side of the dash when the engine was warm. Turned out to be the cam chain/tensioner showing early warning signs so I got it changed and the sound went away. Of course if you're worried about that it can be easily checked with VCDS by looking at Block 91 and 93 in Advanced Measure Values in the Engine menu.