Combines 2366 transmission troubleIJ

First might be a good idea to check wheel bolts; make sure none are loose and causing this noise. When was oil last changedIJ I'd drop the oil and see what it looks like. Metal chunks or excessive glitter in oil would be a bad sign.

Something else you might check for the clanking sound is your final drive couplers. I've had them make that sound when they have not been full of grease.

I had this problem last year with my 1660. The shift rails on your trans are binding_dirty and not allowing it to go into second all the way. Third was nearly impossible to get into gear. Someone had ran it like this previous to me buying it and it chewed up the side of the gear in a few spots causing the noise you are describing. The gear is $700 from CIH. I did mine myself while still attached to the combine. You have to pull the hydro and all attachments off the top of the case. Pull the cover and the end bearing caps and the whole rear shaft comes out. I have never been into a transmission in my life but was able to do this. A few good pieces of cardboard and pull the fan shield off and you can shinney in the right side and do it. Plan on a full day if you have the gear and change the bearings on the shaft when you do it. If it's not a simple final connector which I thought it was plan on running it and fixing it later or go for it now.