grinding in reverse, not the transmission
 

When I go in reverse when I start the car cold it grinds real bad. Sounds like the driveshaft rubbing the tunnel. It also does it just a bit while braking. I can't find any signs of where it's grinding though. When the car has been driven a bit it doesn't do it, maybe just a bit. Never going forward. Does this sound like a carrier bearing?

Nope but it sounds like the gear set is about to let go or the spider gears in the diff..Mine was doing that and i just swaped another diff in..