The clunk ONLY when warm

Clunk/Pop under my seat AFTER car is warmed up (20 min drives).

- just installed FTBR kit and FRPP diff
- just installed stifflers trans mount
- just did energy poly motor mounts
- wheel bearings appear good all corners
- newer half shafts installed last year
- all suspension hardware rechecked, nothing loose
- owned since 2002, 117k miles. Never had the clunk before.

No idea what would make a pop/clunk ONLY when warm. Does it in 1/2/3/4 gear on hard accel/decel or when taking off from a stop in first. No other conditions. I can feel a pop in the floor behind my seat.

Appreciate any suggestions. Didn’t find a “only when warm” caveat under search.


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Could be the "cobra clunk" cause by slack in the diff. The factory rubber bushings will hide it pretty good but when you install solid diff mounts it becomes really noticeable. Mine does it but only noticeable under certain low speed conditions.

I agree that replacing the factory rubber bushings can unmask play/slack in the differential.

I'd agree with everyone else, I just did the bushings as well. I'll take a little clunk over the feeling of the irs wondering around with 20 year old rubber bushings

Does it clunk without moving,

Front of diff,mounts will do this sitting with Lifting clutch to move,

This has been a big issue ,along with gear whine,

Side note,,
Mine is all original except front of diff mounts are poly,
Even just these being added made change in noise from rear,

Thanks for the replies and what I was suspecting. The kicker is that it’s whisper quiet until warm. That’s what had me lost.


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PC03GT said:

I'd agree with everyone else, I just did the bushings as well. I'll take a little clunk over the feeling of the irs wandering around with 20 year old rubber bushings

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I've seen more than a few posts over the years centered around a wandering IRS. I'd also be fine with a bit of clunking over a sloppy IRS.