I have a 03 Explorer with standard climate controls. Now that the cold weather has arrived a clicking noise has also arrived. It is in the dash behind the center stack. It only happens at startup. It sounds like the flap/door that directs the air to the different vents, but it continues as I cycle the switch through the different settings, and it also happened when the switch was left in the off position when parked.

I've looked through the posts and it seems similar but different to the blend air door fix.

So far it has only happened when the temp is below freezing and the car has been parked for several hours making me think that possibly moisture entered the system and froze.
The clicking continues for several minutes at start up, then goes away as the car warms up.

Any ideas?