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Old 02-27-2018, 07:41 PM   #1
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Loud screeching from engine 986

My engine started screeching very loudly today while on a 30 minute ride. Sounds like it's coming from transmission area(Tiptronic) Doesn't matter if it is moving or stopped. Quietens down after giving some throttle but does not go away. Temp OK, no loss of power. Sounds horrible, not sure if it is belt or bearing noise. Help!

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Old 02-27-2018, 08:43 PM   #2
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Belt, pulley or bearing.
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Old 02-27-2018, 08:47 PM   #3
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Pull the oil fill cap and see if the noise goes away. If it does, you may have a torn diaphragm on the AOS, that will create a lot of vacuum in the crankcase, sometimes to the point that it pulls in air past the rear main seal causing the squealing noise. I had that happen on an Audi years ago. It sounded terrible, but was an easy fix.

The tip off to me is that the noise changes when you give it a bit of throttle. Under that condition, there is less vacuum in the intake, and therefore less being transferred to the crankcase through the AOS diaphragm.
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Old 02-27-2018, 09:42 PM   #4
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Thanks, will try tomorrow am! I will report back the results!
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Old 02-28-2018, 04:52 AM   #5
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If you don't get anything from oil cap removal, remove front engine cover to try and ascertain where the noise is actually coming from.
Is the noise RPM related?
I had a belt pulley going and just listening from outside of car you would have thought OH NO IMSB
But front cover off and there you have it. Remove belt and no noise

Good luck
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Old 02-28-2018, 08:27 AM   #6
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Also, if there is a lot of vacuum in the crank case and you can't get the oil cap off when the car is idling the AOS is gone!

Any smoke?
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Old 02-28-2018, 09:08 AM   #7
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Quote:
Originally Posted by kk2002s View Post
If you don't get anything from oil cap removal, remove front engine cover to try and ascertain where the noise is actually coming from.
Is the noise RPM related?
I had a belt pulley going and just listening from outside of car you would have thought OH NO IMSB
But front cover off and there you have it. Remove belt and no noise

Good luck
That's why I suggested to run without the serpentine belt to rule out accessories and pulleys/idlers.

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Old 02-28-2018, 02:09 PM   #8
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That is the exact condition! had to stop engine to remove oil fill cap. Noise went away without the cap! Thanks for the help, parts are on the way!

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