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Weird Noise unable to track down

H

Hmebuildr

NAXJA Forum User
Location
New Hampshire
OK I have a 99 XJ with a 3 inch lift, flow master 60 cat back. The Jeep has no vibrations but I get a weird noise from the rear end.

It only happens when the jeep has warmed up and only when I take my foot out of the gas quickly. It sounds like BRRPPPPP it happens only for a few seconds and it sounds like metal vibrating. I have crawled under and found nothing loose there is no oil leaking from the rear end and there is no play in the driveshaft. It does not happen all the time it only happens when I take my foot out of the gas quickly if I am slowly letting off there is nothing. There is no noise when I get on the gas.

I am at a loss any ideas??
 
If you just out your lift on... The grinding sound when you let off the gas is most likely a drive line vib sound. It happens to mine decelerating in the 40-55mph range. Changes depending on how much crap I have in the jeep. Do an SYE or a transfercase drop for a quick fix. The newer 231 transfercases are prone to vib easier than my older 231. They have a slightly diffrent output shaft set up.
 
Hmebuildr said:
OK I have a 99 XJ with a 3 inch lift, flow master 60 cat back. The Jeep has no vibrations but I get a weird noise from the rear end.

It only happens when the jeep has warmed up and only when I take my foot out of the gas quickly. It sounds like BRRPPPPP it happens only for a few seconds and it sounds like metal vibrating. I have crawled under and found nothing loose there is no oil leaking from the rear end and there is no play in the driveshaft. It does not happen all the time it only happens when I take my foot out of the gas quickly if I am slowly letting off there is nothing. There is no noise when I get on the gas.

I am at a loss any ideas??
Click to expand...

jeeperjohn said:
It sounds like the muffler bearing vibration detector is loose and rubbing up against the tailpipe length adjuster.
Click to expand...
X2 :roflmao:

Specifically, I bet your exhaust is vibrating against (a) the tranny crossmember, (b) the side of the pumpkin, driveshaft, or U-joint/yokes, (c) the leaf spring clamps, (d) the shackle, or (e) the fuel tank heat shield.

My guess... it's when the drivetrain torques to the side slightly due to compression braking, and drags the exhaust with it. It will torque the other direction when you get on the skinny pedal so you won't hear the sound then.
 
It will help if you install a length of flexible exhaust pipe just behind the bend in front of the crossmember. This takes the stress off the header and prevents alot of movement in the rest of the exhaust tubing.
 
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