Under good bearing chirp when raining/humid outside. 4.0

Has anyone else experienced this? Whenever it rains, or is really humid out- I'll get a bearing chirp under the hood. I can't seem to pinpoint, or duplicate it.

 

Serpentine belt most likely

 

Thought that too, but I swear it sounds like a bearing going out. And it doesnt happen every time I start the truck. It's a cheap enough part, I'll throw one at it.

 

Mine has been doing it off an on for a year now, i'll get to it in the Summer

 

Idler pulley bearing.