just a thought, might or might not pertain to yours---grinding noise
happened to me also a while back--I replaced the front diff but it made no
difference in the noise--  --turned out to really be caused by one of the
front wheel bearing-hub assembles.  When I jacked it up to "feel" or
"listen" for a bad wheel bearing it was not very noticeable--apparently the
grinding noise occurs when the wheel spins with the normal weight on it
while driving.  This is not like the old wheel bearings one could
disassemble--this is a sealed wheel bearing hub unit.  Dealer cost is very
high.  A better price can be had at some part store such as
utoZone.  -----Aside from that be sure your 4 wheel drive engagement parts
are working properly.   ------