I did a search and didn't find anything about this. My 126 CCU went bad (I thought). I replaced it with a rebuilt one. Still has this problem:

Works fine in Heat mode and EC mode
In AC mode works fine for a while, good cold air, fan varies accordingly. Then, after a while I begin to get clicking noises. Like the sound that the old cash registers made when printing receipts. It does it sparadicly, then it becomes constant. The funny thing is that if I turn the unit off, it still does it!!!! What's with that?

I seems to be related to something loose. Hitting bumps seems to make it worse.

During this clicking fit the fan and flaps change sparadicly. The A/C is still cold, the fan still blows just changes speeds.

This is one goofy gremlin!