Originally Posted by bobinyelm
What's your best guess based on symptoms?
My best guess would by the transfer case. In particular the needle bearings on the intermediate shaft and gears. The other item could be worn thrust washers letting the gears shift and not mesh in an ideal pattern.
I should have replaced them (bearings/shaft) on my last TC rebuild, but got in a hurry and didn't. The bearings looked fair and the shaft had some pits. The shaft and needle bearings were the only bearings I didn't replace. My visiting in-law, who is a machinist for NA Rockwell, said "yeah, they'll make noise, but should last a while".
I thought I would replace that TC with another lower geared case by now, but 7000 miles later, It hasn't happened.
The whine is noticeable, but not too loud.
The transmissions are very east to rebuild. No special tools needed and no bearing preloads to deal with on reassembly.
The TCs are a little more difficult. Most all the rebuild kits are incomplete and the shafts need to be shimmed to get the correct end plays. The needle bearings, intermediate shaft and thrust washers don't come as a part of any of the $80 rebuild kits.
I cut my own shims from my selection of SS sheet stock, which saved a few bucks.