Just bought vehicle 221k miles on it, did basic tune up, about 3 months later keep hearing a grinding noise that is intermitent, comes and goes, few daysat a time. the sound is coming from what I think is transfer case, down below on drivers side, I have asked 5 transmission shops. No one will help beyond telling me change (Replace) transfer case & transmission, we have checked the drive shaft u-joints, those are fine, also in last week when I put the truck in reverse the trans makes a terrible grinding noise. it goes away when I change back to neutral then back to reverse. Any help would be appreciated, the mechanics out here in Mohave desert are terrible.