I'm getting so frustrated! I just bought an 86' runner 4cyl auto w/170k. It had a loud grinding when ever you let off the gas. Replaced both u-joints and both had rust in two of the bearings, still noise. Replaced the 4cyl 3rd member with a v6 dif. Just took it down the road, still noise! Not the same though, 1st it was constant when you let off the gas and getting really loud. Now that seems to be gone but when you get it up to 50 or so I still have an intermittent grinding, seems to come from the transfer case area. It's only when you let off the gas.
I drained/refilled all the trans fluid. I assume it fills the transfer case too. I'm running out of ideas. God I'd hate to replace that transfer case too.

 

The transfer case gear oil is seperate from the transmission gear oil, so you need to check it out. The noise could be a bad transfer case out put bearing.

 

transfer case fluid is full. How do I check for output bearing wear? Thanks

 

see if you can wiggle the output flange