Whistling Noise

I've got this whistling noise coming from my climate control system in my '05 Silverado 1500. It gets louder as the blower motor intensity is turned up. I took the blower motor out and it's tip top, no whining or anything. I didn't see any leaves or excessive amounts of dirt up in there, or down into the intakes but I admit I can't see everything. I can't find a good diagram of the entire system and I don't want to take my entire dash apart without having a general idea of what it is I'm doing. It's out of warranty so I'm reluctant to take it to the dealer, especially since the only Chevy service center where I live is the equivilant to Ed and Earls Gas/Mat, Bar, Grill, and Service.
Has anyone experienced this or heard of it. Does anyone know where to find a diagram of the climate control system online? Thanks.

if you go to the dealer they can print a drawing of all the internal parts behind your dash
if they dont want to help you because they want to get a service call out of you just pretend you need a dash part in the same area and act like an idiot when you describe it to them and ask if they have a drawing so you can point it out then dont give it back- run baby run
just dont bring your truck when you go

"run baby run just dont bring your truck when you go"   ha ha now thats funny, um is it making that noise behind the a/c control head? or somewhere in the dash by the blower?

I like that ehhget!! lol!

ha ha like that huh???  gotta have fun with it!!