I had a alternator belt that would squeal very badly when cold but after a few minutes when it warms, the squeal goes away completely. The real problem was traced to (might not apply to serpentine belts) an alternator pulley that was worn on the V sides so that the belt couldn't grip the sides no matter how tight the belt was. I could turn the alternator fan by hand and it would slip.

I also read that belts tighten as they warm up and I guess the rubber also softens. Oh, I also replaced the original Conti for Bando as experts recommended for being a "better" belt.
Oreo

My 87 MB 190E 8V belt noise again when cold!!!

I just parked my car about 3 weeks. Before i parked, it is no noisy on the belt. When i start the car this morning, it has very loud noise on the belt.
I drove that car over 1 hour, still had the noisy.

If it is the alternator bearing problem, may i just buy the alternator bearing. Or i need to buy the new alternator.

Please help

Just following the posting!!! Today, just changed the waterpump and quite on my car now! It's the waterpump bearing noisy!!!

My 2 cents: On my 63 corvette i located squealing from bearing on alternator. rather than disassemble, drilled pin hole in end bearing cap and put drop of oil once in a while, stopped squealing instantly! That was over 40,000 miles ago, still running same alternator, charging well. Reminds me of ol generator days when oil caps where on all generators and bearing seldom failed. I guess eliminating oil caps and (grease fittings) is progress? regards to all, and Happy holiday and New Year, Abe G

Over the years I have found two ways to check and see what belt is making the noise. One is remove the belt and then start the engine and see if the noise is still there. On the alternator if you remove the wires it won't charge and also won't be slipping the belt. Jerry