Noisy rear end, 1990 suburban 1500.

[LimpingLizard]

When my suburban has been running a while, I can hear/feel clicking and grinding noises while backing up and turning coming somewhere from the rear of the vehicle. When it is first started up and I make the same moves, it is quiet.

Any ideas of what to look at first?

[chevroletmb]

i'd start with the u-joints. make sure they move smoothly

[LimpingLizard]

Thanks. There's no play in the shaft, would that eliminate the u joints? Also, since it only does it after it is warmed up (and only turning in reverse)? The fluid in the rear end is new, but is a little low and I'm not sure what the mechanic put in when they had it. Perhaps a drain and fill with a good synthetic?

[superbee]

Yes, also if it is a locker or limited slip use some additive, you need all of the help you can get.

[Boogity3]

If it's only when you put it in reverse, it may be your rear differential gears. When you put it in reverse, the gear is being pushed the opposite way and it puts pressure on the weakest part of the gear (the coast side). After time and some hard driving, it could chip away at the gear. This would also make a sound when turning since the rear diff helps the rear wheels turn.