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Old 11-18-2018, 05:04 AM   #21
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Still trying to diagnose.... Research suggested alternator pulley with overrun clutch, ah wa! But upon double-checking mine (from 1997, manual) is solid pulley... so something else yet to be IDed.

By the way, do I have the right pulley? Did all manual cars since 1997 come with clutched pulleys or just later car from 2000ish?
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Old 11-20-2018, 05:05 AM   #22
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Following this - I have the same issue on my 2000S. I rebuilt the motor and it started after rebuild - right around 2500 RPM. I have all new chains/guide rails/vario ramps. I have 5 months of winter to debug and figure it out, but not sure on where to even start!
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Old 11-20-2018, 08:44 AM   #23
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Clutch in, noise gone.... I can not reproduce this noise not matter what rpm with the gear in neutral and car standing still. Only when car is running in gear, mostly in 3rd and 4th on the road, at steady speed with very delicate, slight throttle opening. Taking the foot off or pushing the pedal just a little instantly kills the noise, and back to the slight opening it comes back, very repeatable.

It seems as if combination of UDP, 996 TB and maybe 997 engine mount of recent changes is causing some kind of isolated system instability that the factory ironed out, and it woke up this noise ghost?
The clutch in making the noise go away seems to be pointing to your throw out bearing or perhaps a rattle/vibration in the release arm or spring.

As an aside, I had all sorts of fits with shifting in 1st gear making horrible vibrations until I replaced the single front engine mount. It's a cheap fix easily done in your garage.
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Old 11-21-2018, 09:04 AM   #24
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Following this - I have the same issue on my 2000S. I rebuilt the motor and it started after rebuild - right around 2500 RPM. I have all new chains/guide rails/vario ramps. I have 5 months of winter to debug and figure it out, but not sure on where to even start!
Thanks for sharing this pain, it seems not a serious issue with no performance degradation etc but it sure is bothering!

I take your input basically eliminating those components. I have no record of those valvetrain parts replaced, but several oil changes and filter gut-check in the last 15K miles yielded zero debris to suspect excessivel wear on them.

Letís hope for the resolution soon!
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Old 11-21-2018, 02:32 PM   #25
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The clutch in making the noise go away seems to be pointing to your throw out bearing or perhaps a rattle/vibration in the release arm or spring.

As an aside, I had all sorts of fits with shifting in 1st gear making horrible vibrations until I replaced the single front engine mount. It's a cheap fix easily done in your garage.
Clutch feels good and no vibration/ rattle is felt through the pedal.

As mentioned earlier, I installed new 987 engine mount with new side pads too, so that may not be it... even though it seems as if I started noticing this noise after new mount and UDP installation.
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Last edited by Boxstard; 11-21-2018 at 05:20 PM.
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Old 11-25-2018, 05:34 AM   #26
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When I replaced motor and transmission mounts, found that I experienced a couple of new types of sounds: 1) tighter motor/chasis meant more vibration transmitted to interior of car, making existing engine sounds more pronounced. 2) New sounds from things inside the cockpit vibrating more - at around the 2,500 rpm mark, under certain conditions I heard a new very pronounced buzz - that sounded like it came from engine. After some hunting I discovered it was the mesh hoop insert that vibrated very breifly. Decided to leave it as it adds some character! Hopefully you are experiencing something similar - more pronounced sounds resulting from tighter mounts.
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Old 11-25-2018, 05:50 PM   #27
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When I replaced motor and transmission mounts, found that I experienced a couple of new types of sounds: 1) tighter motor/chasis meant more vibration transmitted to interior of car, making existing engine sounds more pronounced. 2) New sounds from things inside the cockpit vibrating more - at around the 2,500 rpm mark, under certain conditions I heard a new very pronounced buzz - that sounded like it came from engine. After some hunting I discovered it was the mesh hoop insert that vibrated very breifly. Decided to leave it as it adds some character! Hopefully you are experiencing something similar - more pronounced sounds resulting from tighter mounts.
Yes, it seems as if the new mount, together with UDP that drives the accessories at lower speed, promoted or exposed this noise.

My mesh inserts are secured with multiple zip ties (so I wonít lose them knowing how ridiculously expensive these plastics are), so probably my noise wonít be it, but will double-check. Iím pretty sure it comes behind the firewall, thought.

Keep ideas coming! With running out of ideas myself, Iím planning to drive the car with the serpentine belt off to see if I can positively rule out all accessories and pulleys.
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Old 11-25-2018, 09:47 PM   #28
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Yes, it seems as if the new mount, together with UDP that drives the accessories at lower speed, promoted or exposed this noise.

My mesh inserts are secured with multiple zip ties (so I wonít lose them knowing how ridiculously expensive these plastics are), so probably my noise wonít be it, but will double-check. Iím pretty sure it comes behind the firewall, thought.

Keep ideas coming! With running out of ideas myself, Iím planning to drive the car with the serpentine belt off to see if I can positively rule out all accessories and pulleys.
My mesh thingies vibrate as well, definitely a distinct buzz.
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Old 12-20-2018, 03:50 AM   #29
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... I am hearing what seems to be chain noise when giving very little throttle at low rpm....
Hi Boxstard,

The issue you describe sounds very similar to a noise Iím experiencing. I also have a 1997 2.5L.

Every time I Ďfeatherí the throttle, either gradually on or off, I hear a distinct Ďchatterí. Full throttle / No throttle and the noise disappears. Most of the time I hear it when attempting to maintain a steady speed when cruising, but it's amplified at high RPM's when easing off the throttle after a hard acceleration (when joining a motorway for example).

Interestingly, unlike you - I can replicate the noise with the clutch fully depressed and the car stationary, by carefully holding the revs around 2,500 RPM and slowly feathering in a little more gas. Are you sure you canít achieve this ?

Iíve just had my front engine mount changed (for unrelated reasons) which made no difference to the noise.

Did you ever find a root cause?
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Old 12-20-2018, 06:04 AM   #30
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Interestingly, unlike you - I can replicate the noise with the clutch fully depressed and the car stationary, by carefully holding the revs around 2,500 RPM and slowly feathering in a little more gas. Are you sure you canít achieve this ?
Did you ever find a root cause?
Keylime,

Perhaps the noise comes from within the muffler (loose shield) or failing cat..?
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Old 12-20-2018, 06:32 AM   #31
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Originally Posted by jvfante View Post
The clutch in making the noise go away seems to be pointing to your throw out bearing or perhaps a rattle/vibration in the release arm or spring.

As an aside, I had all sorts of fits with shifting in 1st gear making horrible vibrations until I replaced the single front engine mount. It's a cheap fix easily done in your garage.

Good to hear you pointing to the Release Bearing. Bell Housing condensation will rust a release bearing over time and it will rattle. With the Engine running clutch out it will rattle when shutting the engine down. Clutch in no rattle when shutting down the engine. DMF I doubt it's the problem.
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Old 12-20-2018, 07:02 AM   #32
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I noticed the same noise recently. The car is parked, but I had to move it so I drove it around the block. Very noticeable because I don't have the carpet over my engine cover, and my soft top is removed.
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Old 12-26-2018, 03:33 PM   #33
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Hi Boxstard,

The issue you describe sounds very similar to a noise Iím experiencing. I also have a 1997 2.5L.

Every time I Ďfeatherí the throttle, either gradually on or off, I hear a distinct Ďchatterí. Full throttle / No throttle and the noise disappears. Most of the time I hear it when attempting to maintain a steady speed when cruising, but it's amplified at high RPM's when easing off the throttle after a hard acceleration (when joining a motorway for example).

Interestingly, unlike you - I can replicate the noise with the clutch fully depressed and the car stationary, by carefully holding the revs around 2,500 RPM and slowly feathering in a little more gas. Are you sure you canít achieve this ?

Iíve just had my front engine mount changed (for unrelated reasons) which made no difference to the noise.

Did you ever find a root cause?

Still chasing the root cause... and I could not reproduce the noise with the car parked, clutch in or out, no matter how I tried with gentle throttle around the Ďsweet spotí of 2,400 rpm.
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Old 12-27-2018, 10:22 AM   #34
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FWIW-black silicone holds the mesh windscreens securely. Isolating that noise took a while!
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