I have a 2005 SCREW 4X4 with 127,000 miles on it.
Axel 19 = 3.55 Non-LS -> 9.75" ring gear

I bought this truck used about 4 months ago, it has always had a mild roaring noise that has gotten worse. To me the noise sounds like a bad wheel bearing. It is barely noticeable until about 25mph, and gets louder with speed. The noise oscillates and varies with speed as if it were associated with something that is rotating. If I put the truck in neutral and coast down a hill the noise changes pitch slightly but is still there. Also, it makes no difference whether I am turning or driving straight, and makes no difference if I an in 2x4 or 4x4.

Its sounds like it is coming from the rear (hard to tell) so naturally I assumed that is was the rear axle bearings. Thanks to Quintins excellent guide I was able to replaced the rear axle bearings and seals and of course the gear oil. The old gear oil was pretty much black, and the drain plug was covered with a thick layer of sludge, I could see lots of fine metal shavings in the slidge but did not find any substantial pieces of metal in the diff.

Unfortunately, the new bearings made no difference and the noise it still there. I previously replaced the IWE so I know it has nothing to do with that. I investigated the front of the truck and noticed that the front diff has a small leak. There is some old(dry) oil staining all around the region of the front diff where the front drive shaft attaches. And is currently wet with oil at the bottom of the front diff but not actually dripping. I checked the oil level in the front diff and it was low, so I added about 1/2 a quart to bring it back to the level of the fill plug. But again this made no difference.

Does anyone have any ideas what could be causing this problem, or things that I should be looking at? I plan on doing a lot of long distance driving this summer and would really like to get this fixed before then.

Thanks

 

may be a dumb question but, did you check all of the brakes(including rear e brake) for scored/worn rotors? they tend to look OK on the outside but wear quicker on the inside of the rotor

 

Ya, when I replaced the rear axle bearings I had to remove the rear calipers and rotors. They all seemed to be in decent shape. I even got the ebrake working and releasing properly.

 

check your pinion bearing..wiggle the drive shart close to the diff and see if it has any play. make sure you have the back tires off the ground and the e-break off and not it gear.

 

I jacked it up pulled the drive shaft today to inspect the u-joints and they seem to be good. They all rotate smoothly and there is no play. The pinion shaft also seemed to be solid with no play. The only strange thing that I noticed was when I pull the drive shaft out of the transfer case a small amount of fluid dripped out of the socket, enough to make a puddle about 3 inches across.

 

I took the truck into a local tranny shop. It turned out to be a bad bearing in the diff. Not the pinion bearing like most others are having problems with but a carrier bearing. There was no damage to the gears so I had them put in a new bearing set. Cost me $997 but the noise is completely gone.