GMC Pickup Alterator Problem

[pmt]

My 2003 Sierra 4.3L engine pickup's original alternator started making noise (high pitched squeaking) at around 60,000 mi. Replaced it with a NAPA rebuilt unit. Now, with only about 23,000 miles on the NAPA alternator, it has started making the same screeching noise.
Does anyone know what component in these alternators causes this noise? I checked the NAPA alternator warranty - 3 years. Of course, I put it in the truck 3 1/2 years ago. I've always had pretty good luck with NAPA parts before this. Is any auto chain any better than another for rebuilt alternators?
Thanks in advance for any help.

 

[Virtuoso]

Check your belt tension. It could be too tight, putting too much stress on your alt's bearings.

 

[mechtech2]

Auto parts store rebuilds can be iffy.
It's part of the game for starters and alternators.
Bosch rebuilds are pricey, but good.
NAPA may have a pro rated warranty for you onthe present alternator.

 

[Billbert]

Auto Zones domestic alternators are rebuilt by Remy, and lifetime warranty. I have had good luck with Remy's stuff

 

[pmt]

Well, I'm not doing so well on this. I bought an Autozone Gold Duralast alternator(advertised as being rebuilt by Remy). I reused my NAPA belt, because it only had 23,000 miles on it and looked fine. Everything seemed OK at start up and during a short test drive. But within about 30 miles, I could hear what sounded like the accessory belt starting to squeal at engine RPMs above 1500.
So I limped the truck home and removed the belt. The new/rebuilt alternator's shaft rotated with excessive torque - binding bearing I would say, with one spot in the rotation extra tight. (When I bought the alternator, the bearings and rotation felt fine.)
No problem exchanging for another alternator at Autozone. I reused the NAPA belt again - after first checking every inch before reinstalling - looked perfect. Dead quiet for the first 20 miles or so, but then a high pitched squeaking, like a little mouse. Pulled belt - the second Autozone alternator rotates fine - perfectly normal. And the belt shows no evidence of any problem. Voltage when running is right at 14 + volts.
Could the belt slipping when the first alternator started binding have done something that is causing the belt to be noisy now? If so, anything I can do to quiet the belt, or just buy a new one?
On my truck, belt tension is controlled by a spring-loaded idler - it's the original in the new truck when I bought it. Belt tension seems normal. I've also checked the stationary idler - bearing is fine, no noise or looseness. The squeaking noise is present whether A/C is on or not. Any suggestions, or am I stuck with buying a new belt?
Thanks in advance.

 

[mechanicx]

Is the belt maybe a tad shorter than OE and applying too much tension? Is it hard to get the belt back on? Are you overtightening the alternator mounting bolts and distorting the case? I can't think of any other reasons that you are eating so many alternator bearings so fast.

 

[Chris142]

Old belt on a new pully. Replace the belt

 

[Jim Spahr]

Sounds like the belt and belt tensioner need replacing.

 

[mechtech2]

Ribbed serpentine belts wear and seat in the grooves of the pulleys too deep.
They will not hold full tension at this point.
You may have a weak tensioner, or a bad belt.
And sorry to say, the alternator is not 100% safe yet.

 

[Herz]

Always replace the tensioner and idler when changing belts or alts and waterpumps in my opinion.

 

[SteveSRT8]

or at least lube up the tensioners. They an run a LONG time if you run some high end synthetic gear oil into them.

Just don't overdue it.