Becoming more and more pronounced is a loud growling coming from somewhere on the rear end. Guessing somewhere on the axle but not sure.

It happens when accelerating under load sporadically as well as just sitting stopped and idling in traffic in drive, when it can get REALLY loud with the brakes fully depressed. If i let up on them the intensity will decrease or go away. then start up again at some point during acceleration (or it doesnt). If I shift to N or P it will stop, but begin again sometimes when I shift back into D and accelerate and then disappear/reappear. Sometimes becomes really pronounced in R with wheel cranked all the way left or right, but also does it just driving along straight. It sounds like muffled heavy marbles swirling around somewhere, pretty odd. rumble strip-esque. driveshaft, u joints, axle are stock d35 i think with 180k miles on them, so all need to be replaced I'm sure.

Might be a bearing, but happens while stopped. could be a ujoint but happens while stopped too and it's not exactly clicking its a variable loud low rumble.

 

the first 2 things I would check is the clearance between transfer case and crossmember, as a sagged trans mount will allow them to contact, should be +1/2"
and engine mounts, especially LH they always fail 1st, engine can flog around

 

thanks. I just replaced the trans mount with a poly mount so it should be good, but i'll check. there's nothing directly below the tcase... the cross member is just behind the trans oil pan and i don't see the exhaust contacting it. why would engine mount noises be coming from the rear axle?

 

must be the skidplate it rattles on, maybe you dont have one?

a dud engine mount shouldnt be making a noise at the rear axle

however, as you have noise when not in motion, while no parts near the rear axle are rotating, that must mean it is a vibration, or coming from elsewhere

....you could have more than one fault of course, most older XJ have a few worn parts

did the noise start after you changed the trans mount?

do you have ABS ?

 

 

Are you sure it's coming from the back? Other than that, sounds like a brake booster problem. Can you get another guy to explore while you're sitting there on the brakes?

 

 

Have you checked the fluid levels in the rear axle and transfer case?

 

I filled the t case last week and filled the dif when i did the pinion seal 6 months ago.

 

torque convertor bolts loose might be worth checking, even though it will be spinning in P and N, it will be under load in gear

 

You might try putting someone else behind the wheel and pressing
on the brakes and getting underneath yourself to better chase down the noise.

 

OK. now I am thoroughly stumped. I stopped the car as i began to hear the loud grumble from the rear again. I put it in neutral, drive, park, reverse. the grumble remains. i put it in park, get outside, go underneath and the sound is nonexistant. I just hear exhaust, but nothing noticeably banging. the sound isn't there. inside, in any gear, while stopped or driving, I can hear it the resonant grumble like something rolling around in the gas tank or something. But when i go underneath, it's unable to be located anywhere. Can't hear it at the trans, muffler, cat, tcase, diff. come back inside and it's rumbling away. I am convinced now this must be an exhaust issue but i'm totally stumped. It's possible the noise pollution outside is diluting the low end rumbling noise, or that i can't hear it over the exhaust. but inside it definitely has moments of clattering metal on metal and overall rumble. coming from the very rear of the vehicle.

I'm thinking the next step is heading off to a great exhaust shop, i can't imagine they'd want to take the time to track this down though. Since I can't see any exhaust pieces banging, I'm thinking that my driveshaft U joint might be on its last legs, and the vibration at idle (I have poly mounts) is causing it to chatter. It did growl before the poly mount though. I know the joint is 180k old and clicks and clacks into gear. Or a bearing somewhere is totally done and disintegrated and rolling around due to vibration.

 

If it happens when you are stopped, it is very unlikely to be a u-joint, bearing, or any rotating part related to the rear axle.

I think you have something resonating the chassis (body) at the right frequency. This can basically turn your body into a drum if the frequency is right. These types of resonant vibrations can be very apparent inside, but non existent outside. They can also fool you completely as to their source, because the vibration could be anywhere - but it can resonate at a different location.

Don't be afraid to put a work glove on and touch the exhaust member when the noise is happening, to see if you "feel" a similar frequency/vibration in the exhaust. Do the same with the transmission and oil pan and fuel tank while you are at it. Basically, you are feeling around (instead of listening) for a similar frequency vibration.

 

use a mechanics stethoscope all over

what about the spare tyre & mount?

rear hatch tight?

chuck a hole heap of blankets around inside to see if it alters the acoustics

 

I fixed the issue.

I could not hear the grumbling from outside the vehicle. So i followed Jordans advice. pinpointed it to the gas tank. I got it up on a lift. sure enough, exhaust pipe just grazing it up where i can't see. but i can feel it with the glove (it's hot use a glove!). There is no noise being under there, but for some reason it causes a giant ruckus inside the cabin you can hear the metal on metal inside but not outside. then at idle it will do this lovely acoustic thing where the whole cabin resonates and induces fear into passengers and mechanics. but it's just a simple little exhaust love tap. i actually can see it at the right angle but it's too hot to get my head up there while it's on. So when it's cool I was looking underneath everywhere, and obviously it wasn't making contact while turned off so i never really saw it.

Cut it off, clocked the tailpipe out, welded. Noise is gone.

Thanks everybody! always satisfactory to track these things down and make it right.