I'm not on here often but I fixed mine by dropping the glove box (as if you were changing the filter) and then running through the modes to see what was happening.
Turns out the actuator door behind the glove box was skipping a tooth...since I didn't want to tear the dashboard out I found someone on the internet that had a fix.
What I used was just a piece of scrap 3 wire and casing I had laying around (like what you use for house wiring) and bent it into a kind of question mark shape and just hung it in the vent holes where the door comes down and closes.
https://www.youtube.com/watch?v=WbzOkVOhMJ4
When the door closes it hits that before it can start making the clickity click noise that was driving me nuts.
My wife is constantly changing the heat/modes and it was getting really irritating...been that way for 6 months now and still now clicking...