I Agree with Chris. Jack each side up one at a time. Then see if you can rotate the rear wheel at least a full turn in each direction twice in each direction. See if it locks up at any time. If it does mark a place on the tire and see if it always locks up the same place. I would also get a clean 5 gallon bucket and drain the transmission. I would listen for metal falling in the bucket as well. Start there first. More questions?