Np231 transfer case grinding noise

So I just sold my 231 with hack and tap sye on it and the guy is having trouble with new vibes and grinding. I never had that problem in my jeep. I did searching and a lot suggests that it is the linkage out of adjustment.
It came out of a 93 with 4.0 aw4 and went into the same year make and model. The only difference is his has a 6"ish lift and mine has a 4.5". He didn't ope it up so I know nothing inside could be the problem. I'm trying my best to help him out and fix the problem so any suggestions would be greatly appreciated.
And I hope this is okay in the OEM tech board

New vibes could be cuz the drives haft isn't long enough for his extra lift I'd think, or u joints and grinding how? Goin in 4wd, coming out or when in 4th and driving?. Linkage would be a good place to start

He says it does it while he is driving and stopped in gear. I relayed the driveshaft theory to him so we will see.

not gonna have anything to do with the driveshaft if it's doing it when stopped.

look for causes of a misfire if it "vibrates" when sitting still.
look for a bad motor mount as a possible cause while you're there.

Here is what he says
-I already checked the motor mounts and it runs fine. At a stop the it feels like the case rattles loose but everything is tight. I get vibes and it feels like its from the whole case not the rear and it just sounds like it grinds while I'm driving some times.

Exhaust rattling on cross member?

It could be a broken gear tooth in their rattling around.