Alarming Noise Coming From Under Jeep

[Arthurius]

2006 LJ Rubicon, 77k miles, Auto trans

Background: I recently did a 75k mile refresh of my t-case, differential, and engine oils before a trip to Moab. During the Moab trip we did moderate offroading, but did make an attempt at Top-Of-The-World that had a lot more bangs on the underside than I would like. Also, during the refresh, the studs for the Mopar trans mount sheared (fuck) and I had to buy an Anchor mount, which has induced some minor vibes. More on this below.

After bringing it home, I noticed around town I would occasionally hear a rattling sound coming from the Jeep. It eventually got worse and I was able to diagnose it (or at least notice it most) happening at low speeds when turning, and most noticeably when reversing. Backing out of my driveway would recreate the sound almost every time, for example.

It has now started making this racket shortly after startup, even when in park and not moving. I haven't driven it enough to know if it will go away at speed because I'm about worried about the case. However I'm not sure that there's anything moving in the T-case while in park and stationary? That has lead me to question if it could be the exhaust, trans, or something else?

Here's a running video:

You can see in the video it doesn't seem to be coming from the engine or trans, and it loudest when listening from the rear of the T-case.

Interestingly, after I shut it off today I tried to rock the Jeep back and forth, and this knocking sounds EXACTLY like the racket when the engine is running. Could this be my T-case about to grenade?

Heres the non-running video:

I first rock it gently from the sliders and then more aggressively from the hardtop.

 

[macleanflood]

I'd certainly be looking at the exhaust to rule it out...

-Mac

 

[GregBelleville]

Do you have an automotive stethoscope? I'd be poking one around the transfer case, exhaust, etc to see if I could isolate the source of the noise.

 

[OldBuzzard]

I first rock it gently from the sliders and then more aggressively from the hardtop.

The aggressive rocking sounds like a duck!

Grab the exhaust pipe and yank it around, in several places. If it's rattling, it should be easy to find, since the idling engine is enough to rattle it. Might as well eliminate that possibility first.

Try to rock the engine and shove the tranny side to side, in case it's a motor/tranny mount.

 

[Arthurius]

@GregBelleville I do not have an auto stethoscope, but if the $10 one on amazon is worth a damn then i will probably pick one up this coming payday.

Does anyone know if the chain in the T-case spins while parked?

I have looked up some t-case noise threads and some of the noises sound similar to my issue and they had low/no fluid in the T-case and/or the chain was worn. Most, however, occur when driving. I'm concerned the T-case may be the cause because it was recently flushed and filled by yours truly.

 

[BlueC]

I'm with the others saying knock on the exhaust first. I suggest taking your hand and bumping the cat around, cold of course. A loose core will make a similar rattling noise.

After that, you could try rolling in neutral engine off to see if the noise is present.

 

[GregBelleville]

@GregBelleville I do not have an auto stethoscope, but if the $10 one on amazon is worth a damn then i will probably pick one up this coming payday.

Does anyone know if the chain in the T-case spins while parked?

I have looked up some t-case noise threads and some of the noises sound similar to my issue and they had low/no fluid in the T-case and/or the chain was worn. Most, however, occur when driving. I'm concerned the T-case may be the cause because it was recently flushed and filled by yours truly.

That's what I bought and it works just fine.

 

[OldBuzzard]

I do not have an auto stethoscope...

They're handy, but you don't really need one. A piece of copper tubing, rubber hose, metal rod, long screwdriver, or socket extension can all be used. Press one end against something, and your ear at the other end.

Does anyone know if the chain in the T-case spins while parked?

The front driveshaft is attached to the bottom sprocket, so the chain spins any time the front axle is turning, not when parked, no matter what gear the TC is in.

 

[Arthurius]

So after taking a mallet to much of the exhaust system and not finding the rattle, I used an automotive stethoscope and I am fairly confident this noise is coming from the T-case. The only time i received the rattling feedback was when i probed the t-case, the exhaust was a very low-humming rumble.

Interestingly, this sound happens when the Jeep isn't moving which is contrary to all the other threads about T-case noises i am seeing.

What are my options for servicing the t-case? Can i open and inspect the chain and other internals while it is still installed? Can the chain be replaced without t-case removal? Or is it better to remove the entire unit and rebuild it? Seems premature as the Jeep only has 77k miles but i got it at 43k so cant vouch for the PO miles/usage.

Any tips are appreciated!

 

[BlueC]

Interestingly, this sound happens when the Jeep isn't moving which is contrary to all the other threads about T-case noises i am seeing.

If the input shaft and/or driveshafts are not moving, then nothing is moving inside the T-case, so I don't think the T-case would be producing the noise while sitting still idling. In the same situation the transmission is moving, or at least parts of it, and could be transmitting noise through the T-case, so how sure are you this noise is coming from the T-case?

BTW, you mentioned that you just did a drain and fill, what oils did you use? Just making sure you didn't put a gear oil in the T-case.

 

[RHanna]

I would have guessed exhaust like others but it also sounds like something isn't tightened down enough. Like the skid plate or transfer case mount.

You could also disconnect the rear drive shaft (and the front if you want to be extra safe) and run it in drive to see if the noise is truly gone while the driveline is running.

 

[macleanflood]

Is it possible you're getting some sort of harmonic noise from the exhaust into the transfer case?

Maybe you need to check or replace your transmission mount?

-Mac

 

[Arthurius]

BTW, you mentioned that you just did a drain and fill, what oils did you use?

Mopar ATF-4, i pulled the quantities from the sticky thread here on the forum. I have pulled the fill plug and some fluid dripped out so i know the case is filled.

I would have guessed exhaust like others but it also sounds like something isn't tightened down enough.

Maybe you need to check or replace your transmission mount?

I am thinking this as well. This weekend I'm going to pull the skid and inspect my trans mount install, the studs fully sheared off of the old one so i think i may have limp wristed the nuts holding the mount down when i reinstalled it. I am starting to really miss the Jeep, i haven't driven it for well over a month now out of caution.

The probing with the scope revealed a hole in the side of my muffler, but i held the probe directly on this hole and only heard the low hum that can be heard in the background of the OP video.



The racket only came through the stethoscope tubes when i put it on the housing of the t-case. I probed the bellhousing and pan of the trans and didn't hear much, maybe a slight echo of the main racket, but when i held it to the t-case it was very loud. It was louder when held to the front of the t-case near the front driveshaft mount, thats why i suspect the t-case most.

 

[Rickyd]

Mopar ATF-4, i pulled the quantities from the sticky thread here on the forum. I have pulled the fill plug and some fluid dripped out so i know the case is filled.





I am thinking this as well. This weekend I'm going to pull the skid and inspect my trans mount install, the studs fully sheared off of the old one so i think i may have limp wristed the nuts holding the mount down when i reinstalled it. I am starting to really miss the Jeep, i haven't driven it for well over a month now out of caution.

The probing with the scope revealed a hole in the side of my muffler, but i held the probe directly on this hole and only heard the low hum that can be heard in the background of the OP video.

View attachment 566312

The racket only came through the stethoscope tubes when i put it on the housing of the t-case. I probed the bellhousing and pan of the trans and didn't hear much, maybe a slight echo of the main racket, but when i held it to the t-case it was very loud. It was louder when held to the front of the t-case near the front driveshaft mount, thats why i suspect the t-case most.

If your jeep isn't moving then nothing in the tcase is moving. The only way you could possibly get that to happen is if you put the tcase in neutral and the transmission in gear.

If the motor is running then the torque converter or input shaft move in the transmission when stopped. You have sound resonating somewhere it isn't originating from.

 

[Arthurius]

You have sound resonating somewhere it isn't originating from.

Fuck. Lol I suspected that to be the case

This is making me REALLY consider getting a seperate trans mount like the Savvy setup. This whole trans mount/skid plate/crossmember/locker mount/shovel is some of the dumbest shit I've ever seen engineered.

 

[BlueC]

You have sound resonating somewhere it isn't originating from.

That's my thought, and that can be a bitch to track down.

 

[BlueC]

@Arthurius Apply the KISS method. I'd start by looking for loose bolts or broken mounts. Then, for the reasons above, I'd assume the T-case isn't producing the noise, so it's somewhere in front of it. Maybe chock-up the tires really well, or lift them off the ground, and run it in gear and see what happens.

 

[Arthurius]

I was hoping it was a blown cat. When I was listening around i checked the front two near the engine and the third, but wasn't able to definitively find the source. The noise is most noticeable after the engine has been running for a bit which makes me wonder if it is media from the cat that went bad, and starts to rattle after warmup. Many have said the cats can fail around the 70-80k mark from what i have been reading.

That combined with the new trans mount makes me think the issue isn't internal to the drivetrain and it can be isolated to the trans mount, the mount bracket, or some exhaust racket.

I will keep you posted!

 

[D's Jeep Wrld]

I'm just here to drop my 2 cents and no reading of the rest of the posts
I thought I was in for new pistons since the stock piston skirts tend to break off and it sounded just like your jeep
Longstory short it was the 4k mile old (new) cats I had on there that were making it sound just like piston slap.....

 

[Arthurius]

Well damn, its not the exhaust, its definitely in the driveline!

This weekend i went out and started it up as it sits first, and even after it fully warmed up it wasn't making a sound. I banged the exhaust and probed with the stethoscope but couldn't find anything. I put it in drive to pull it out of the garage and do some neutral roll tests, and the clanking immediately started. Putting it in reverse caused the same. In park it was quiet as a church mouse, which is contrary to the sound being produced while in Park in the OP video.

I was alone in the garage that morning so i couldn't look for the sound while it was in drive. I put the rear axle up on stands and started her up to put it in drive but, nothing. No sound, no clanks, shifted thru PRND all without issue, wheels turned fine. So it seems the sound is most associated with the drivetrain being under weight/load, though it is possible to be created while in park, just not 100%. While on the wheels and put in drive or reverse, the sound was extreme.

What next? I removed my belly skid to start removing driveshafts but neck pain made me decide to wait for guidance. Should i try a flush of the transmission? I purchased all the materials to do so but never got around to it before Moab, only the engine, diffs, and t-case were serviced. I dont think this loud of a clanging will be fixed with a simple fluid change, though?