2002 Sierra squealing after startup

[SonofaSierra02]

When I crank my truck I am getting a pretty loud squeaking noise that will eventually go away after about 5-10 minutes of driving. I took off the serpentine belt and inspected it; there were no cracks and it still looks like new (I replaced it around 2007 I think). So while the belt was off i started turning pulleys to see where the squeak was coming from. I was able to hear some squealing when I turned the alternator pulley. Does this mean my alternator is getting ready to go bad? I have been watching my voltometer and have not seen any low readings yet, and I put in a new yellow top Optima battery within the past year. Thanks in advance for your advice and suggestions!

 

[DBMedic]

Squeaky pulleys

Mine did the exact same thing. I had two culprits: the A/C belt and the idler pulleys. After a while, the squeaking just got worse, and squeaked longer. Check your pulleys and A/C belt.

 

[07 classic sierra]

Fan clutch

I don't know if you solved your noise issue yet but I use to have a dodge ram with a fan clutch before and that is where my noise was coming from sprayed WD-40 and the noise went away until it snow or rain got in there again, if your truck has a fan clutch might look there?

Also wondering about all the Ford ad's on this GM web page?