l just replaced the front end differntial and axel because it was making a grinding noise and the shop l took it to said that that was what the problem was but before the grinding noise would stop if you put it in four wheel drive but now it sounds fine when its not in four wheel drive but makes the grinding noise when you put it in four wheel drive. whats wrong with it now?

Transfer case maybe?

maybe the problem was in the transfer case instead of the differential,looks like they should have been able to find that problem,if they changed that out and it did not repair it, id let them know about it,that was a useless repair if its doing the same thing that it was,good luck.