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Alternator noise


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Had my alternator rebuilt last fall. Did removal and installation myself. Worked fine, but I thought there was a high pitched hum coming from it. Told the guys that rebuilt it that I was parking it for the winter and they said no problem, whenever you decide to pull it again, we'll check it out.

Pulled it out the other day and took it to the rebuild shop. They threw it on a high tech machine and it was cranking 180 amps.There was a small noise, but not the one I kept hearing.

They tore it apart and could'nt find anything wrong other than hot spots on the brush rings. They cleaned the brushes, and changed the bearings. They said that putting the noise aside, that I probably needed to see if I had a short that was constantly making the alternator run, and to check my battery.

Well, I had just put a big new Interstate battery in when I did the rebuild the first time, but I took it to check it out and it had a bad cell. Got a new replacement battery and reinstalled the works.

Noise is still there but I've decided it is coming from underneath somewhere, but if I hadn't pulled the alternator the second time I might not have found the battery problem in time to save the rebuilt from burning up.

That stupid noise never changes pitch except when you come to a stop, and then there is just a little surge down and then right back up.


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Kent, I had the same problem. I wish that you posted this before you pulled your alternator. I had a whine and the SHOP could not find it and basically told me I was wacked. I swore it had a whine. Well, I bought american made front and rear bearings (SKF) pulled the alternator and said, do me a favor, replace the bearings with my bearings and give it back to me, they charged me $20... Result, WHINE GONE! The same rebuilding shop had rebuilt it about 2 years prior. The front bearing was made in CHINA (YUK). If I rolled it in my fingers it would occasionally jam/bind up, there was either dirt, a rough spot or a flat spot in the bearing. Mike

Early on sailors navigated by the stars at night and the North star became the symbol for finding ones way home. Once you know where the Northstar is you can point your ship in the right direction to get home. So the star became a symbol for finding ones way home or more symbolically even finding ones path in life.

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Did you start the engine without the belt installed ?

If so, did you still hear the noise. ?

If not, then it's likely one of the two belt idler bearings, the power steering pump or the AC pulley bearing.


2008 STS V8
2016 Colorado Z71
1970 Corvette LT-1 Coupe

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Typical stock alternators AND ac compressors on NS cars make noise. Had them both replaced under warrantee on my car. They still make noise. This is not an excuse or a panacea for your problems, just a fact that I've seen many times.

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I had a slight hun similar to what you described when I first bought my 92 eldo, turned out to be the water pump....replaced it, no more whine

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