Squealing from under hood – bad alternator?

[Andrew]

Hi everyone,

I have a 2002 Pontiac Grand Prix GT (Ohio car) and just recently I have heard a loud squealing noise coming from around my belt/pulley/alternator area that would squeal constantly. I immediately thought bad alternator bearing, so I swapped out the alternator for the alternator of my old car, a ’99 Grand Prix (same part, I checked about 7 times to be sure). But now, I’m still hearing a squeal, not as loud or constant as before, now it only happens when I take my foot off the gas pedal. It stops if I accelerate or brake, but squeals in between. And I heard a noise that I can only describe as chains being dragged along the ground. I think this alternator is going bad too, but I just wanted to see if anyone has had an issue close to or even spot on to what I’m having, and could give some incite into this. Thanks.

Topic

[Its me]

Try a mechanics stethoscope to find a bad bearing.

-Karl

[Matt]

From my experience it’ll be either:

-an old or worn out belt is slipping
-the belt is contaminated with coolant or oil and is slipping
-a bearing in a tensioner or idler pulley is worn out
-the tensioner itself is worn out

[Author]

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