Ok, I just recently bought my Dad's '02 Silverado from him (truck in sig) and it's got a weird belt squealing issue. Not every time, but most times, when I turn the engine over there will be a loud, momentary belt squeal as soon as I release the key in the ignition. It does this whether the engine is hot or cold. Also, when I turn the AC on, it blows cold but the belt squeal noise happens for a loooong time at initial AC turn on (I assume as the compressor is charging the system?) and then it happens again for a few seconds each time the compressor cycles.

My question is, are these squeals the result of belts needing replacement? Or am I looking at needing to replace the tensioner pulley and possibly the entire AC compressor?

 

Since the majority of the noise is present when the A/C compressor is on then I would target the belt that drives it and the idler pulley that maintains pressure on that same belt, the bearings tend to dry out over time due to heat exposure.