Alternator high frequency noise

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JB0702

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Hello,

I am not sure if it’s relatable but I don’t know where to ask so it would be great if anyone can help me.

I recently purchased a remanufactured alternator with new brush and bearing and all for my car. I haven’t installed it but when I turn the pully, there is a really high frequency noise from alternator. The noise is not constant and seems to be louder when I turn it clockwise. Can anyone help me why it’s making a noise like this? And will it be safe to use on my car?

I have filmed the noise. I played it to my dad but he said he can’t hear anything since he can’t hear high frequency noise due to his age but me and my wife can definitely hear it. One of my friend said he thinks it’s brush and commutator noise. Thank you!

 
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There's no commutator on an alternator. Commutators have gaps that separate them into several sections. The brushes run on slip rings that have no gaps and have just one section for each slip ring. Some alternators don't have brushes at all.

Do you know which direction it runs in the car? As far as I can see from the video, the fan is designed to run in the clockwise direction.

On many alternators, the brush / regulator assembly can be unscrewed from the back quite easily. If you do that, you can see if the noise comes from the brushes
 
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Thank you for your reply. I believe it turns clockwise in the car. I am not sure if I can unscrew the alternator as it seems very complicated at the back. But do you think it is okay to use?
Thank you!
 
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I'm too old to hear anything on that. It looks fine to me.

If it had dead bearings or something seriously wrong with the brushes it wouldn't spin like that.
 
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I have pretty good hearing and I can't hear anything. Am I missing it?

It's not uncommon for the brushes to be causing whatever noise you might be hearing. New brushes haven't bedded in yet. The running engine probably drowns out anything from the alternator. A squeal or grinding noise from the alternator is bad, though, and would suggest bad bearings...unlikely if it's rebuilt.
 
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I put the sound file into a frequency program and this is what I am getting. The high pitch noise is at around 15kHz and quite consistent when the pulley is turning. All the parts inside the alternator looks quite new so maybe I should install it and see how the brushes settle in. Thank you!
 

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