Shrieking Noise

My '99 Miata has been making a shrieking noise if the engine is warm and revs fall below 1000 RPM . If I accelerate to 3000 or so RPM--usually in
3rd gear, drop the clutch and let the revs fall back, it goes away. Belt dressing has helped. It may be related to generator belt. I had it replaced about 6 months ago after it shredded, but the noise did not develop until 1 mo. later. When I drop revs, lights dim a bit. Other threads and maybe shop manual indicate possible problem with the clutch--big $$$. But could it be the belt itself, or a shaft of whatever is connected? Anyone have a similar experience?
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Sounds to me like the bearing in your alternator may be going bad. It could also be a bad belt tensioner.
--
Boreal
2001 LS 6 speed Silver/tan, Sport Suspension w/hard rear sway bar
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That happened to me too, a few weeks ago. In my case, it was a neighborhood cat stuck under the hood, near the front of the engine bay. When the revs dropped, I could hear the shreiking. When the revs climbed and engine noise got louder, the shreiking went away. Eventually, the noise went away altogether.
-- Larry
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On Thu, 26 Oct 2006 21:28:27 -0400, pltrgyst wrote:

Geez Larry, that's pretty graphic. Perhaps the feline was more comfortable at higher rotational/vibrational rates. I don't even want to picture why it might have stopped.
Now, my black/tan 2002 LS has also been shrieking, since Thursday when I took her off the road for the impending winter and shut her in the garage.
Every time I walk by I hear this pathetic plaintive plait to be let back out, to be running free, back out in the wind, in the sun, in the cold even, even with the top UP, but out nonetheless...
Frank
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frank wrote:

Sorry to hear you must live in a cold climate (sigh). Today started out a bit wet, but the 6 am morning temperature (yes, I did say 6 am on a Saturday) is already 67. Looks like a top-down day here in NC.
My '04 MSM is a daily driver, so I enjoy it all year long. No hard top either, although I am intrigued by the new retractible top coupe. Will be hard to beat the MSM though, I really like it.
Oh yes, shrieking noise...sorry, got carried away. Yes, I had a shrieking similar to the description above on my '99. Mine was from a new belt, and yes, after a month or so, it started, indicating to me that it was loose. I tightened it up and was fine after that. I also had an alternator go bad on the '99, however it did not make any noise, just quit.
Tom
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KKennedy wrote: > > My '99 Miata has been making a shrieking noise if > the engine is warm and revs fall below 1000 RPM. > If I accelerate to 3000 or so RPM--usually in 3rd > gear, drop the clutch and let the revs fall back, > it goes away. Belt dressing has helped. It may > be related to generator belt. I had it replaced > about 6 months ago after it shredded, but the noise > did not develop until 1 mo. later. When I drop revs, > lights dim a bit. Other threads and maybe shop > manual indicate possible problem with the > clutch--big $$$. But could it be the belt itself, > or a shaft of whatever is connected? Anyone have a > similar experience?
I had exactly the same problem with my '93. It sounded like the noise was coming from the clutch but that was not the problem, it was really the alternator belt. It sure didn't sound like it was coming from the front of the engine though.
I think new belts stretch a bit the first month or two. My '93 started yowling like that a couple months after I had the belts replaced. For the first ten minutes or so it would shriek embarrassingly coming off stop lights from just over idle to about 2500-3000 RPM when it would finally catch, plus you could tell that the alternator wasn't being driven by the way the headlights dimmed while the belt slipped, and brightened as soon as the noise stopped as the belt caught.
On the '93 there's an adjuster bolt in the bracket for the alternator which you can adjust to tighten the belt so it won't slip. If you turn it with a little wrench the alternator hinges away from the engine, tightening the belt. It's underneath the alternator so I had to locate this bolt by feel but there was a picture in my Haynes manual that gave me some indication of where to grope around. I was worried about overtightening the belt and putting excessive lateral tension on the alternator shaft so I only tightened the adjuster bolt about a half-turn at a time for a few days until it ceased to screech. That cured the noise problem for about a year, then one day it sounded off again, so I popped the hood, turned the tensioner bolt another half turn, and never had any noise afterwards.
I've got a '99 too now (beat-up paid-off '93 + drunk in pickup lo-miles shiny new[er] '99 + car payments) but I haven't looked under the alternator to see if they use the same bracket; my guess is yes. I hope I've diagnosed your screeching problem correctly; a couple twists with a wrench sure beats paying for a clutch job!
Yours WDK - snipped-for-privacy@ij.net
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wrote:

I had the same problem on my 99 after having the belt replaced. After a while it had stretched. Adjusting the tension to tighten it up a bit made the screetching go away.
Jon Weinberg
| email: jon at JonWeinberg daht com | web: www.JonWeinberg.com
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It was the alternator itself. Gave way in a rainstorm, of course, couldn't have happened at any other time. (Machines do not like me.)

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Had something like that happen years ago on a then new 71 Camaro. On the first major road trip the altenator bearings started screaming. I was lucky enough to find a Dealer's shop open on Saturday night! (Large City, in warrenty)

in
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