I have a 2005 Dodge Ram 2500 with 87k. It is now time for the defroster every morning, but I heard a strange clicking sound this morning while it was on, as dimming of my interior lights.Any thoughts?

Might consider dropping the blower motor out and take a look at it...

I agree with Mike, drop the blower motor and see what's going on. I had a piece of napkin from the glove box fall into the bird cage and make an awful racket.

I know this is an older thread but I too had this problem about a year ago. Drove me nuts and final I dropped the blower motor. I'll admit that I almost threw the motor assembly because it looked like a dead creature had died inside the basket. Turns out it was insulation from somewhere which concerned me because it was quite a bit and had no idea where it came from. Anyway, I cleaned it out and put the motor/fan assembly back and all was good until this past Saturday when I turn the air on. Same clicking/vibration! Haven't looked yet but I assume the same issue. Any ideas of where this material is coming from and should I be concerned about the fact that somewhere in my truck its missing this material.