Jay, you are a STUD! I will precisely peform your troubleshooting and see what occurs. By the way, your questioning made me recall something the Service Advisor mentioned in his email to me after I very cordially voiced my concern over having this type of repair with a 3 + year old car... He said the following:
"The part which went bad on your Armada is not something we see very often, but with the heat we live in here in Arizona, it is not usual to see plastic parts break or become brittle. The complete dash of your vehicle has to come out to replace this component."
As the Advisor stated, I do live in Arizona. Does the fact he mentions a plastic part help you determining the cause. Are the doors of the heater unit plastic? I can't imagine the entire heater unit is plastic, is it? Just a thought...
Good evening. I hope you are having a nice evening.
I performed your troubleshooting routines. The only time I could get the clicking noise (which comes more from behind the radio console than the glove box) is when I reduce the temperature dial down from 72-70 degrees all the way to 60 degrees. During the temp downslide, if I stopped at 65 degrees the clicking usually didn't occur; however every time I turned the dial one more turn to the left advancing the temp down from 65 degrees to 60 degrees the clicking began every time. This scenario was true for AC on and AC off and in each of the modes. Essentially, if I left the temp setting alone, I could scroll through all modes, AC & heater without the clicking noise ever occurring.