Trouble diagnosing cause of alternator noise

[Kingy]

Has anyone else had a history of noise coming from the alternator? It's a high pitch whine with throttle input but only at very select rpms. It is really noisy starting up cold then kind of disappears as the car warms up. Once warm, I can only hear it occasionally at certain rpms and it's very annoying.

I've replaced the alternator as the other one was shot but i'm still getting the noise. I started getting the noise after a very hot period last summer when the original alternator died.

I took it to a mechanic who thought it sounded like a vacuum or boost leak but I've bought an electronic stethoscope and can only hear the noise at the alternator location.

Could it be a crack or some anomaly within the bolt holes connecting the alternator to the block.

I'm really having trouble with it. I tightened and loosened the belts etc but am still getting the noise. WTF could it be?

The good news is that the engine sounds fantastic and there's no knocks, low vibration or anything, I just want to get rid of this high pitch sound.

 

[jet150]

Is it the belt? or the pully?

 

[AKKO]

To clarify is it alternator itself whining audibly or are you hearing it through the stereo / sound system?

 

[Kingy]

It's not interference as I can hear the noise from the engine bay and with the radio off. Definitely coming from the alternator area

 

[trotty]

Sounds to me it's the idler pulley. If the alternator has been replaced and its still there then is gotta be something else.

Easy fix is disconnect the alternator belt and start the car. If its still there ur problems lie elsewhere. My aircon power steer idler is making a similar noise.

 

[Kingy]

Nah it's not the idler pulley. It sounds fine. I pulled apart everything tonight and reinstalled the support bracket the alternator fits in, the idler pulley and the belt. It's still making the same noise. Very frustrating.
I think it's the alternator. I used the stethoscope and the only place I can hear the noise at idle is at the alternator. I'm thinking it might be the bearings/brushes in the alternator. This is very coincidental since it's a new one. I might have to reco my old one and install it.

 

[marksanne]

Are you sure the tensioner pulley is mounted straight inline with the crankshaft- and alternator pulleys? This week I replaced my alternator and I made a mistake putting the tensioner pulley-bracket-mount (that part that holds the power steering-hose in place, mounted with 2 bolts) underneath the tenstioner-bracket instead of on top. The belt went on fine, I didn't notice it, until a day later I heard a soft high pitched noise. Looking from the top I saw my mistake and corrected it. Now everything is quiet again