Yep sounds like a water problem. Same thing happened to me. Had to replace all bearings in the rear axle and a axle shaft to the real bad wear from the bearing. $700 later I pretty much had a new axle. I also had the whining coming from the real bad bearing and shaft.
I had my rear end rebuilt at 120K and my gears didn't look new, but they were passable. I had some whining noise under all driving conditions and when I would drive by the concrete barriers on the highway I could actually hear a loud clicking sound. The pinion bearing was completely wasted and all the bearing material came out in the fluid and it looked like anti-seize copmound. I also had some other bearings going bad because there was some wear on the end of the axle shaft and it had started to groove. Had it rebuilt with factory parts and truck drove great. I could tell the difference as soon as I hit the gas, I could actually squeal the tires again. :
I think the whining sound is from the transfercase since it only happens in 4wd :bigthumb: . If the gears have been replaced, They'll turn the fluid a greyish color due to the black coating wearing off the gears themselves. :dunno: Just throwing some other possibilities out there
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