The clicking noise is from your Air Blend Servo motor (controls hot/cold mix). The gearteeth that control the flap have slipped off. It is really easy to fix, the only problem is removing the whole dash to get to it.
Easiest way is to make sure the heat is maxed all the way up, i.e. slam the red button a million times before u start the car (can be on or off), wont make the sound - leave it like that and wont happen again