While driving today my silverado made a terrible almost grinding noise. I stopped immediately and saw no visible problems. When I shift into reverse it makes the same "almost" loud grinding noise without moving. When shifted into drive it will move forward a bit then makes the same noise. Very bad. Had it towed to the house. Any ideas?

 

Was this issue ever diagnosed/repaired? I am currently having the exact same issue with my 00 GMC Sierra 1500 4x4.

 

see if you can pull the transmission pan and run a magnet underneath

if you have metal shavings its time for a rebuild or new transmission