On my 2000 4R I have a sound that is almost the exact same kind of sound that you would get from mud tires on pavement. The tires on it were Toyo A/T's and they were 5 years old and cupped so I figured that was it.
So here's what I have done to try to stop the sound:
1. Bought new tires...Yokohama Geolander HTS which are just about street tires and that didn't make any difference.
2. Changed the front & rear differentials + transfer case oil and replaced with Amsoil Severe Gear 75w90 - no difference
3. Greased all u-joints - no difference

So now I am out of ideas and the sound has not gone away or even slightly got quieter.....and I can't pinpoint where its coming from either...just underneath.
Please help with any $.02 or ideas......cuz it's drivin' me crazy!
Thx

 

It could possibly be your wheel bearings. Did you check those?

 

really man black font just dont work

 

I know I didnt notice it at first lol

 

Ok...more info: jacked up the back end and ran it. The sound is definately coming from the rear end. Wheel Bearings or Pinion....how do I tell?

 

unbolt your drive shaft from the pinion and check for excessive play.

 

Pull the rear third, have the gears inspected and re-install on an ARB locker using all new bearings.

Put it back in and see if the noise is still there. If so then it's the wheel bearings.

OR while the axles are out to pull the 3rd just replace the wheel bearings also.

It could be a U joint in the rear driveshaft. Pull the driveshaft and drive it in 4wd. If its gone then it's in the driveshaft.

 

Best way is to get a mechanics stethescope from an autoparts store. Have someone to put the vehicle in drive and you get under it with the scope. Go from the rear diff to the outside of the axle tubes to find where it gets louder. If it's at the end of the tube then most likely it's the bearings, if it's louder at the diff then it's something internal. However, if it IS the diff then I'd just go ahead and replace the bearings and seals at the end anyways just for future security. "Do the job once, not twice"

 

I'll assume you've checked to see if the axle seals perished. 3rds, I've read, are notorious. I had to have my rear carrier overhauled. Pinion bearing was the culprit. Very labor intensive. I had the work completed at a local shop. $900. Good as new now.

 

Or, just put the truck in neutral and get a good grip on the drive line to check for the play.

 

^^ what he said.

 

Why did nobody list the best fix for this kind of stuff?


Turn your music up.

 

OP, when my pinion bearings where going out, they sounded more like a big rig's exhaust when it's downshifting. Maybe you can relate the two since they are semi-similar.

What I did to replace it was just replace my whole 3rd member. $900 to replace the bearings or $100-150 to just pick up a good 3rd. I chose the $100-150 option.

 

It's the pinion bearings.......found a 3rd member for $250 from these guys!
http://www.yodajims.com/

 

great people over there! got my TJM from them, very nice and very helpful! definitely recommended!