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Discussion Starter #1
had major service to suspension couple months ago, that dealt with all the all noises and clunks ... except for one, deep clunk sound at road bumps mostly when driving slow coming from front/middle of the car. Had car inspected at few places and none could diagnose the fault. It wasn't very frequent and not so annoying so I managed to live with it.

Last week as it started to get more cold in the morning, another sound came up, just at start up in colder days, a sound as if a loose part is fitted around driveshaft and rotating undercar hitting the body.
occures only once and lasts for like a minute or few, goes for good after car warms up.

This made me re-think of the older left clunk... that too seemed to lessen when car is warmer.

Thinking of it:
- eleminated possibilities of starter motor related, it starts up without any sign of struggle
- eleminated possible causes in engine/tranny as there was not any sign in performance
- had peddal floored few times while looking at engine, and it looked good in place without movement, so engine mounts should be good too.

>> left my doubts at tranny mount.

had car inspected at dealer for that sound, and although car was left to next morning to fire cold, they couldnt duplicate the case (was a real warmer morning), and said there is no issue in engine/transmission/suspension!

I asked change of transmission mount (at my request), and they argued for no need, but I i sisted (my $$). I left the car and came at end of day picked the car. To my surprise I wasn't charged for labor, and discounted almost %40 off mount price. Only realised why the genearouse treat when I got home and looked at the old mount they packed in my trunk, the rubber had totally broken of metal surface!! ...
and both sounds mentioned above are gone for good (a clunk, and the grinding below car at cold starts)

hope this helps
 

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What is the difference between the old mount and the revised mount?
The revised mount eliminates a resonance that most if not all of us have while driving around 70mph with the original mount. I only learned about this last year and bought the mount and longer bolts you need to install it.

GM 92237122 - Revised Transmission Mount
GM 92138719 - Transmission Mount Bolt, Long (x2)


When I read the OP the symptoms matched what I recently experienced with my G8. It ended up being a heat shield hitting one of the headers when the car was cold. As soon as the car warmed up, the vibration went away. It took a day to figure it out.
 

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I also updated to the newer part number mount and bolts. Completely eliminated the hum noise I heard on the highway. It was cheap, maybe 20-30 bucks I think. Easy to change the mount, worth the corrected outcome.
 

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the revised mount eliminates a resonance that most if not all of us have while driving around 70mph with the original mount. I only learned about this last year and bought the mount and longer bolts you need to install it.

Gm 92237122 - revised transmission mount
gm 92138719 - transmission mount bolt, long (x2)...
Thanks for the information
 
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