Drivetrain noise

[Chamberpains]

I like TruckerMatt's run down. Just a couple more things. Put the small hammer away. Thats for your lawn mower. It's a tractor you need big tools. Get a BFH, Big F'in Hammer. Don't crush things but give them a thump. Some thing won't move or rattle without a healthy whack. If it breaks or moves, then it was definitely gonna break or move going down the road.
Also get a very large pry bar and a 2nd set of eyes to check your u-joints, carrier bearing and engine mounts. Your hand will only expose very worn out things. You need some leverage to check for the starts of things going wrong.
Rawze learned the hard way of not catching a driveline issue soon enough. You'll have to find that story. Its a good read. That was probably one of the worst driveline failure messes I've heard of. Im gonna venture a guess that it was not from a lack of looking, but from not putting enough pressure on things to expose the little things. But thats only a guess. He may have more insight in to it.

Also have an oil sample pulled from trans and both rears. Sounds like you can very easily have something going in any of them. Rears failing often make scratching noises.