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THIS DISCUSSION / SOURCE-DERIVED OVERVIEW
Discussion summary
YOUR RESEARCHGrinding/scraping noise when decelerating, only in 2nd gear and only when cold
Reported or suspected cause
25 year old mufflers
Reported cause
No successful repair reported for this finding.
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Reported cause · Original poster
Turns out it was the 25 year old mufflers with loose internal baffles and rusted bolts/clamps making the 'grinding' noise.
Grinding/scraping noise when decelerating, only in 2nd gear and only when cold
Frequently discussed work
Check transmission and drivetrain components
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Suggestion
Considering the RPM, the downhill scenario, and the fact that the noise disappears after warming up, I’d suggest checking the transmission and drivetrain components.
Grinding/scraping noise when decelerating, only in 2nd gear and only when cold
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Leading evidence: '25 year old mufflers' (1 discussions report identifying this cause; no attributable repair resolution). Across 1 matching discussions, the most frequently mentioned possible cause is '25 year old mufflers' (1 discussions; 1 report identifying it and 0 suggest it). The most frequently discussed action is 'Check transmission and drivetrain components' (1 discussions). For that action, 0 discussions report a resolution and 0 report an unsuccessful attempt. No action has an explicit, attributable resolution report under the current rules. These are forum reports and suggestions, not a confirmed diagnosis.
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Performed · outcome unconfirmed · Original poster
Replaced the mufflers and also replaced the clamps and bolts, and now the noise is completely gone.
Grinding/scraping noise when decelerating, only in 2nd gear and only when cold
Check transmission and drivetrain components
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Unsuccessful attempts
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Explicit resolution reports before identified causes, performed actions and suggestions. Within each level, matching component labels precede direct query mentions and inherited thread context; successful versus unsuccessful discussion counts, owner confirmations and independent discussion support determine order. This is not a probability of success.
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Suggestion
Considering the RPM, the downhill scenario, and the fact that the noise disappears after warming up, I’d suggest checking the transmission and drivetrain components.
Grinding/scraping noise when decelerating, only in 2nd gear and only when cold
Frequently discussed actions (2)
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Check transmission and drivetrain components
No successful repair reported for this finding.
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Unsuccessful attempts
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Suggestion
Considering the RPM, the downhill scenario, and the fact that the noise disappears after warming up, I’d suggest checking the transmission and drivetrain components.
Grinding/scraping noise when decelerating, only in 2nd gear and only when cold
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I posted about this a few months ago (
https://rennlist.com/forums/996-foru...when-cold.html
), but I wanted to ask again with some additional details and hopefully I can be pointed in the right direction.
1999 996 tiptronic with about 95k km.
Only when the car is cold (ie. first drive of the day or after it's been sitting out in the cold for several hours) only when I'm in 2nd gear and let my foot off of the gas, as the car decelerates it makes a grinding/scraping noise from the back. It's more prominent when I'm on a downhill and the car is rolling down without my foot on the pedal. I think I feel a bit of a vibration at the same time.
RPM is <3000pm when this happens. The tip would auto shift into 3rd if RPM gets any higher, then the noise doesn't occur even when decelerating.
The sound goes away when I press on the gas pedal to accelerate.
When the car is warmed up after a few minutes of driving, this issue goes away completely and the car cruises/decelerates smoothly when I let go of the gas, without making any strange noises.
Given that it's related to whether the car is cold or warmed up, is it something to do with the oil needing time to get pushed around? Or maybe something with the mufflers resonating at a certain RPM (they do have cracks along the seams and loose internal baffles)? A loose heat shield?
If it was a more serious mechanical issue (eg. a bearing going bad, the differential or transmission, etc) wouldn't I expect to hear the noise worsen at higher speeds, and at all temps?
It's made this noise sine I bought the car back in July, and it hasn't caused any performance issues. Only every once in a while I notice it on my morning drive and it bugs me for a while before I forget about it again.
Thanks in advance!
Considering the RPM, the downhill scenario, and the fact that the noise disappears after warming up, I’d suggest checking the transmission and drivetrain components. The connection between cold weather and the noise could be related to lubrication or fluid viscosity.
Given the cracks in the mufflers and loose baffles, the sound could be related to the exhaust system. I'd recommend taking a closer look at the mufflers and the associated components.
Thought I'd leave an update in case anyone else was experiencing the same thing. Took mine to a shop to have the water pump/tank/pulleys preventatively replaced and asked them to have a look.
Turns out it was the 25 year old mufflers with loose internal baffles and rusted bolts/clamps making the 'grinding' noise.
2500-3000rpm must've just been just the 'sweet spot' for the mufflers and parts to vibrate enough to make the noise noticeable. The reason I thought the noise went away when warm is because as my tiptronic warms up in city driving it upshifts early just before 2500rpm and I was always driving under it.
Test drove the car in manual mode and yup the noise was there around 2500-3000rpm at all gears, even after warming up the car.
Replaced the mufflers and also replaced the clamps and bolts, and now the noise is completely gone.
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