I have a 97 CTD cab/chassis with a 12' cargo box (cube) mounted. Getting ready to turn 500K miles. I have noticed a grinding noise coming from the rear end. When it first started it would only happen when in reverse but lately I have noticed it when going forward at very low speeds especially when making a tight turn. This has been an off and on problem for quite a while but is definitely more prominent now. Checked the rear end diff fluid and it is full and not discolored and no obvious leaks. I have not torn anything apart yet. I am not mechanically inclined in the least. Just thought I'd see if anyone else has had anything similar.
Thanks

 

Do you have an LSD (limited slip) rear axle?

 

I suspect you are thinking clutches in the ls. I think so also. I'd pull off the cover and if you don't need the ls and don't have any sign of serious metal in the gear oil you can probably refill the rear end with amsoil. The noise sounds like worn limited slip clutch plates and the synthetic oil may lube the plates enough to stop the chattering but it'll act like an open differential. It might get you another 100k. However the best fix with a rear end making noise with that many miles is to bite the bullet and have it rebuilt.

 

Thanks for the replies. I found the problem and you won't believe how simple it was. Nothing this easy ever happens to me.
I jacked the rear end up so the rear tires were off the ground and let it idle in reverse so I could actually get out and listen.....**** noisy diesels : )
I could still hear it in drive and reverse but only on the driver's side. So I popped my drivers side wheel simulator off and when I took the center cap off I heard this clanging noise. The part of the center cap that actually covers each of the lug nuts were all loose making noise every time I moved it.
So I got back in the truck and idled it in gear without the simulators on and voila no more noise. I lost my passenger side center cap along time ago so that explains why that one was not making noise.
Pheewww What a relief!!!
There is a way to tighten the "lug bolt covers" on the center cap but it takes a torx screw driver in a size I do not have so I haven't fixed it. But now that I know what the noise is I don't think it will bother me as bad.