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Please help with whistling sound


After putting a new alternator on, this whistling sound occurs. I've asked 2 other forums, and even taken it to a porsche shop in my area. Nobody can even give me a starting point on this thing. I hope that maybe somebody here will be able to point me in some direction. Thank you.
Old 06-13-2018, 07:04 AM
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I don't hear a whistling sound in that video, sorry.

Is it while on idle, or during revving?
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Old 06-13-2018, 09:25 AM
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Originally Posted by kdjones2000 View Post
I don't hear a whistling sound in that video, sorry.

Is it while on idle, or during revving?
it's making the whistling the whole time I'm revving it in the video. It happens at about 1100 rpm, and it seems to disappear when not at those low rpm. Also, I very much appreciate you responding.
Old 06-13-2018, 09:45 AM
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That sounds more like a metallic rattle or scraping than a whistle to me. Are you sure that your alt pulley and fan are tightly secured and not rubbing anything or moving on the shaft? How is your belt alignment?
Old 06-13-2018, 10:18 AM
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That sounds more like a metallic rattle or scraping than a whistle to me. Are you sure that your alt pulley and fan are tightly secured and not rubbing anything or moving on the shaft? How is your belt alignment?
I'm fairly sure that the alternator is situated properly, although I suppose one can never be too sure. I stethoscoped the alternator, and it sounds like the whistling is in it or the area. In regards to the belt, I have no clue about that. I just put it back on there, and hoped it was right. Could it not being placed right produce such a noise?
Old 06-13-2018, 10:29 AM
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The alt belt ribs must be properly aligned with the ribs on the pulleys. I know on mine, it is usually hard to get that belt over the ac compressor. I would start with checking the belt alignment and positioning on the pulleys. Also, they will squeal if not tight enough. If you had to use the old alt pulley on the new unit, make sure it is tight.
The noise I heard MAY have been belt squeal, not sure though.
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Old 06-13-2018, 06:15 PM
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- How long have you owned the car? Is it new to you?
- What prompted changing the Alternator? Was the other one making loud noises/bad bearing?

I suggest removing the alt/AC belt all together and see if the sound goes away? If it does, you know it is definitely one of those components. Does the sound go away with the AC on or off?

I have seen issues with the alternator or AC compressor mounting bolts being broken and causing issues.

Best of luck
Old 06-14-2018, 07:02 AM
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If the belt is squealing and slipping the battery gauge will be jumping around, too, because the alternator won't be charging.
Old 06-14-2018, 02:50 PM
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Seems like it may be slight slipping of the belt at low RPM's, and it goes away at higher revs.

Try tightening the belt some more, removing it, and fiddle around until you can pinpoint the issue.
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'88 951S - with LBE, Guru chips, 3Bar FPR, 1.3mm shimmed WG
3300 lbs, 256 RWHP, 15 psig boost
"Certified National PCA Instructor" Hoooohah!
1987 924S 944 SPEC racecar - '88 pistons/DME, short 5th
Old 06-14-2018, 03:09 PM
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