Have an 02 Sierra 5.3 Z71, 30 k miles. When I put the air or heat on , there is a couple second loud sqeel under the hood, goes away then does it again. After a few times it happens less and less and will go away while driving. I changed out the serpentine belt ( the original ) no change. I guess it is a pully or bearing ??? Anyone have experience with this, Oh yeah...sometimes happens when starting. Very annoying, but as you can see , the truck is not driven too often. Any help appreciated. Thank you

 

Did you change the main belt or the ac belt? Possible ac belt and or ac belt tensioner? Seen the ac belt tensioner seize.

 

I changed the serpentine belt, and the tensioner seems ok...tension is good, spins fine. ( is there 2 belts on a 02 sierra, thought there was only 1 main belt ) Both the AC and the heat work well, its just the initial squeel from under the hood when the fan motor is turned on, I did not think the belt would fix it...its more of a metal on metal noise than a belt squeel. kinda like a bad bearing ..the noise will come and go for lets say about 15 minutes of driving ,only for short durations, then I wont hear it anymore till the next trip

 

Yes there are 2 belts - change the A/C belt.

 

thanks for the replys, found a u tube video for changing the ac tensioner and belt, so looks like I got a saturday project. Thankfully not a pricey or difficult lookin job. thanks again for your time

 

turned out to be the a/c tensioner, replaced it and put on a new belt also, truck sounds great again. thanks for the info.

 

Cool glad you got it fixed and thanks for posting your results!