Any help would be greatly appreciated! I have a 01' xj and I have this low roar type hum from what seems the front end. At about 65mph I get this hum and it gets a little louder till about 75mph and then gets no louder. If I'm in 4wd the hum goes away unless you take your foot off the gas and it comes back. As soon as you step on the gas again it goes away. In 2wd it is always there no mater if you're on the gas or not. Heres what I've done so far. Rebalanced the tires, changed front drive shaft u-joints, changed fluid in front, rear diffs and changed fluid in transfer case. I had a real good mechanic look at the front axle u-joints and they appear perfect. I'm ruling out wheel bearings because the sound goes away when put in 4wd. Everything runs great, drives straight and no vibrations to speak of. Just this noise. Could it be hubs? Gears? anyone else ever have this problem? Thanks!

 

did you have the mechanic check out your dshaft ujoints or just the axle u's?

 

Yes, he said the rear u-joints were good too. I replaced the front shaft u-joints because I thought that may have been the problem, but there was no change. The front diff was leaking at the pinion yoke so when I replaced the pinion seal I did the u-joints at the same time.

 

did you check the wheel bearings they can sometimes make some nasty noises before they go just jack it up and grab the wheel there shouldnt be any play if there is most likely your bearings are going bad

 

I checked the wheels for movement. Ball joints, tie rod ends and bushings all look good. No movement at all in any direction. The steering stabilizer needs to be replaced though. The seal is blown and oil is leaking from the housing. That's all I can find though. Seems like everything works good. Transfer case makes no noises when shifted in to 4 high or low. Front diff makes no wierd noises. No clunks, grinding or creaking. I'm totally lost for direction on this one! I fear it's something I'm the transfer case.

 

did you rotate your tires as well? try taking out your front ds and driving and see if it helps anything.

 

how is the fluid level in the diff and is ther any ply in the axle yoke? I would have to agree your bearings are going

 

Fluid in the diffs is good. I just changed it in both and the old stuff didn't look that bad. I rotated the tires last week and I didn't notice any flat spots or uneaven wear. I'll pull the front ds off this weekend and see if it helps. Could it be a pinion bearing? I did have some leakeage and changed the pinion seal, I should have changed the bearing while I was in there. Dangit! Thanks for your help everyone!

 

Unit bearings/hub assy.(wheel bearings) need to do mine and have the same noise that has evolved into a squeek when turning. 97+ use them cost around 90.00 ea

 

If it was a wheel bearing, could the noise disappear when shifted into 4wd? Say, if the bearing tightens up when 4x4 is on? I hope thats all it is. An afternoon changing wheel bearings sounds a lot better than a transfer case issue.

 

yes it could be a pinion bearing but its hard for any of us to tell there are somany different things that make that noise if bad. put it up on stands and investigate. Find some one to help if your not sure what your looking at or feeling for!!!! thats about the best way most of uas can help

 

Front drive shaft rubbing on factory skid plate ?

 

Thanks for all the input about my problem. I have talked to a few people now and the concensus is wheel bearings. So I am going to replace both sides this friday and hopefully this fixes the problem. I figure it's probably due for new hubs anyway at 100,000 miles. Or will need them shortly. I will post again after I do the job and let you know if that was the issue or not. Cross your fingers.

 

I am so bummed out! I changed the front hubs last night and the noise/vibration is still there. On a good note though the drivers side hub was on its way out. There was a little play in the bearing. Took it up to my local mechanic last night and he is pretty stumped. He said it could be a drive shaft out of balance, something in the transfer case and even a warped brake rotor. I know one of the rotors is warped, but I can't see how that would make that much noise and then stop when I shift into 4wd. Thats what has the mechanic really stumped. When shifted into 4wd the noise stops. He does not think it's a bearing of any sort. He also does not think it's the pinion bearing. I have a feeling I'm going to be chasing this noise till I sell the Jeep. I'm running out of money fast so I may have to just let it go. I'm going to pull the front drive shaft out tonight and see if that changes anything.

 

Dude you may want to look at your front drive shaft rubbing---- If you been wheeling your heep you may have bent the cross member up enough were your front drive shaft rubs on the cross member ever so slightly & when in 4wd the noise goes away... Trust me I chased this issue down on my sons stock heep... If the cross member is not bent look at the tranny mount bushing if it is worn out it will make everything sag causing the same issue..A easy fix & alot cheaper than unit bearings
Hope this is the gremlin your chaseing