Rear End Noise, Already Replaced Bearings

My 1997 Jeep Grand Cherokee has a rumbling, slightly metallic noise coming from the rear of the vehicle. (I do not believe this to be tire noise since I rotated the tires and no change).
This noise starts at about 25 MPH and is more pronounced when the vehicle is under load. When you take your foot off the gas the noise greatly reduced.
I have replaced the wheel bearings which did not help.
The visible gears show no wear and there was no significant metal filings, etc in the differential case.


Where next?

 

Have you checked the u-joints on the drive shaft ?

 

Sounds like the exhaust is touching something. Good luck

 

U joints don't seem to have any excessive play, no visible signs of exhaust rubbing anywhere.

Maybe the main differential bearings? Can they be checked without by just pulling the caps off?

 

As far as bearings in the axle I would also look at those on the main pinion. If you have the differential out and the ring gear out of the way you can check those bearings for play and roughness by turning the pinion by hand.

Have you ran this low on oil with leakage on the wheel seals - what is the history on it?

The bearings we're talking about typically go for a lot of miles without problems.

 

differential side bearings can't be seen without disassembly...likewise the pinion bearings. you might be able to feel a bad pinion bearing by turning by hand...but not always. the things is this...load sensitive diff bearing noises are normally pinion bearings...side bearings are more noticable sometimes in turns. i normally have someone ride with me and try to pinpoint right left or center and how drastic is the change when loading and unloading the driveline. the proof is in the pudding, when it's taken apart, there's NO mistaking wheich part is bad. some care and understanding of differential assembly is required...as long as you are only replacing bearings, old shims can be reused without measuring but pinion nut torque is absolutely critical...so a few special tools may be needed as well.

 

Thanks for the replies. History on the vehicle is 118,000 miles, differential never run dry as far as I know.
This noise has been present for a long time, but worse now.
It sounds like its time for a pro to analyze the sound or just ride the tide and hope it doesnt blow up on me in the middle of nowhere.

 

it will eventualy fail big time and could cause alot of collateral damage. since it's pretty noisy now and getting noticeably worse, now is the best and probably cheapest time to do it...

 

If your sure it's hypoid related, it might pay to shop salvage yards for assemblies. It's the right age for a bargain.

 

differential bearing problems in 90's jeeps with high mileage are common and buying a used one could end up the same place. replacing diff bearings isn't that expensive.