92XJ with strange sound from rear...

After I shift into third, I can hear an odd whining noise from the rear...sometimes if I let up on the gas it goes away..sometimes it doesn't. Typically though, if I take it up to speed and then let it cruise a bit, the sound goes away. Any thoughts?

Take a ride in my 95 and youll hear whining and other unhappy noises. Been like this for the last 10K or so. Do a fluid change and inspect the gears also look for metal particles. Might give you an idea of how worn it is.

It may be differentials...although, I did just have the differential serviced, the oil changed, and I specifically asked if they saw any metal in the old oil. They said it was clean....Thanks guys

The noise might be amplified or exacerbated by other things, such as stiff u-joints in the driveshaft, or some kind of sympathetic vibration. It's a good idea to get down there and check everything you can - shock mounts, exhaust brackets, u-joints etc. Some 8 1/4 rear ends can be pretty noisy anyway, though. Mine has howled for years. It was a little worrisome when I got it at 110K miles. It's a little louder now at 248K, but a little less worrisome.

A change to synthetic lube can sometimes quiet it a little, but if it's not too bad I would just keep an ear cocked for change, but wouldn't worry too much.

I also notice that it's louder with the seat down, among other things, so if you've just put the seat down or just cleaned 10 years of crap out of the back, it may not be the rear end itself that's changed sound.

Thanks Matthew. I have not climbed underneath and checked anything yet. I will do that!!

Whine under load (as opposed to under coast) is usually a sign of a worn rear pinion bearing.

Before diving into the diff, though, I would change the oil, examining it for metallic particles, etc.

Does the diff leak at all, either from the cover or the pinion seal?

x2 on the 8.25, at 180k with no rear seat or carpet mine is quite loud.