Weird driveline noise...

I'm wondering if anyone has had a similar symptom and figured out the cause?

Noise: Sounds like the exhaust (or something) is vibrating on the underside of my rig. It also sounds like gear noise, or the transfer case chain rubbing the side of the case.

When: I ONLY get this noise right when I've let off the throtal.

I'm trying to figure out if it's coming from either the transfer case, or rear end although it DEFINETLY sounds like it's coming from right under the floor.

I also noticed my rear exhaust hanger is non existant, which is why I'm thinking it might just be the exhaust vibrating against something, although I don't see any wear marks. My driveshafts have new joints, and I do not have a SYE. I have about 4" of lift, but had this same noise (although less noticeable) when it was at stock height. I'm about to do an SYE and will rebuild the case at the same time if I can get some response that people have had the same noise coming from the TC.

Thanks for any pointers!
Bryson

From the description of where the sound is coming from I'd start looking at the transmission mount and u-joints at the transfercase. Grab the driveshafts and give it all a wiggle. That'll help you home in on the worn part and replace it.

XJCreeper said:

From the description of where the sound is coming from I'd start looking at the transmission mount and u-joints at the transfercase. Grab the driveshafts and give it all a wiggle. That'll help you home in on the worn part and replace it.

Click to expand...

Transmission mount is fine and U joints are all brand new. It had the noise before and after U joint replacement. I've completely ruled out the driveshafts.

Really hard to say without listening to a noise like that. It could be the t-case chain really loose rubbing the insise of the case, but that loose a chain should skip and pop in 4wd. It could be the slip splines on the t-case output shaft and slip yoke, they can make a sort of slight growling noise at coast, like just when you let off the gas. Installing an SYE would take care of that. It could be the exhaust, but you should be able to find where the exhaust is real close to the floor, keeping in mind what the torque of the engine does to the exhaust position right when you let off.

Tough to internet diagnose.........good luck finding it.

Goatman said:

Really hard to say without listening to a noise like that. It could be the t-case chain really loose rubbing the insise of the case, but that loose a chain should skip and pop in 4wd. It could be the slip splines on the t-case output shaft and slip yoke, they can make a sort of slight growling noise at coast, like just when you let off the gas. Installing an SYE would take care of that. It could be the exhaust, but you should be able to find where the exhaust is real close to the floor, keeping in mind what the torque of the engine does to the exhaust position right when you let off.

Tough to internet diagnose.........good luck finding it.

Click to expand...

Exactly. I thought it might be the slip splines (since it's a 99), but I had packed the yoke full of wheel bearing grease and still the same result. But that "growling" noise you described is exactly what I have although it's not so "slight." Ever since I lifted the heep it's been much louder.

This is why It'd be great if someone here that has had a similar noise under the same condition which might help me pin point it. eace:

Bryson said:

Exactly. I thought it might be the slip splines (since it's a 99), but I had packed the yoke full of wheel bearing grease and still the same result. But that "growling" noise you described is exactly what I have although it's not so "slight." Ever since I lifted the heep it's been much louder.

This is why It'd be great if someone here that has had a similar noise under the same condition which might help me pin point it. eace:

Click to expand...

I had that growling noise on mine before I installed the SYE, it was very irritating trying to figure out what it was. I ended up running it in gear with the axles on jack stands to figure out what it was. SYE took care of it.

Since you have a 99 Im gonna guess you have an 8.25 which are know to be noisy.First check your angles,and take a look at the pinion bearing,they are known for that also.

I'm going with the rear exhaust hangar. Right after mine broke off it started making a rattling noise when idling at a light.

My jeep makes the same noise, at the same time. Take out the rear driveshaft, put the jeep in 4x4 and drive around in front wheel drive. I'll put $10 on it being the slipyoke rattling around on the output shaft. At lifts over 3.5" on the newer cherokees the slipyoke is engaging on a dangerously small amount. As soon as I took out the rear driveshaft the noise went away. Just waiting on the parts to install my SYE now.