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high pitch whirl from engine compartment

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2003 C4s. I'm hearing a high pitched whirl sound at low speeds from the engine compartment. Likely masked at higher speeds. I've listened to the engine at idle and think the whirl sound may be coming from a replaced alternator or a pulley or the engine belt was that replaced at the same time. It's high frequency and maybe I should just turn down the setting on my hearing aids? Best to all....

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belt dressing can keep the sqealing noise away,,,

Thanks, good point that I hadn't thought about. Used lots of that stuff on my old '62 Chevy. The noise doesn't really sound like a belt squeal to me, more of an electrical motor whirl. Hard to explain. It's just barely there when the engine is idling, and I don't think I could capture it with a digital video. I was serious about the hearing aids. The high frequency sound is most noticible to me on acceleration when I'm actually wearing hearing aids. Wish I could pin this down a little better. I think it must be characteristic of the alternator. But I never heard it before the old alternator was replaced. Thoughts?

Here's the car...

Edited by judgejon
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Does the noise change dependent on current draw? Lights and A/C off versus on.

long drive today, same sound with or without a/c, lights, etc. It must be generic to the generator I guess. It's a Bosch, purchased from Sonnen late March. is this an expected sound, or maybe my hearing aids are just too sensitive. thanks to all, jl

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If you want to rule out the belt dribble a little water on it while it is at idle. If it is the belt the water will make it slip at a different frequency or make the squeal, if it is belt noise go away for a minute.

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Attach an Ohm meter to your battery while the engine is idling, makesure its puting out the correct voltage which should be anywhere from 13volts to maybe 15v max, then turn the engine off and check the battery with the Ohm meter to see if its at 12 - 13 volts.

If your getting a whine from the alternator, it could be that your battery is crapping out and the alternator is working really hard to power everything OR you have a rebuilt alternator that needs to have its warranty exercised ;-)

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  • 3 weeks later...

turns out the noise was caused by the alternator pulley. being replaced tomorrow at my local indy. similar problem just noted over on 6speed, seems this high pitched pulley noise is not that uncommon. thanks to all...

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Interesting. I have never had a pulley fail unless damaged from someone. Can you find the details of the failure please and post them here? I would also check the condition of the battery under load to see if it's on it's way out.

P.S. Never use belt dressing. It causes a huge mess and never solves the problem of a noisy belt just covers up the problem for awhile.

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belt dressing was great on the older v belts when necessary, but usually the problem was that the belt was simply too loose. I do not believe that it is recommended to use belt dressing on the newer serpentine belts..might cause a slippage and that could be big $$$.

Re the pulley, the mechanic said he could hear the high pitched sound coming from the pulley when he tested it. I'll post the details for sure.

Battery is a big Interstate MTP-93, installed new in late March. now hooked up on weekends to the Charge-omat II.


here's where the pulley lives. I read that the new 997C4S will be getting a reflector stripe again, but a bit narrower.

Edited by judgejon
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