I had the original alternator replaced as it had a bad bearing like noise at idle. Noise level went down as RPMs increased. The rebuilt replacement does the same thing. The mechanic says it is the alternator because if he removes the electrical connections to the alternator and just runs it on the battery, it goes away. Obviously not an alternator bearing then, but what could it be?

 

Sounds like possibly a short in the charge wire or a ground problem internally. If you replaced one for the same thing already, I would say trace or run a new charge wire. Is it more of a hum or squeal?

 

It sounds almost like a power steering whine. I will have him check the charging wire.