Here's a video of the issue. Can't feather the clutch it goes from 0-100%.
Well you realize that makes a great deal of difference for anyone trying to imagine what might be going on.
In that case, then by all means, split the tractor. I've heard a similar sound many times with dry clutch button disc plates. I believe it's occurs when the buttons wear down to a point where the metal jacket around and behind the buttons come into contact with the pressure plates. The sound comes while the disc and pressure plates are turning at different speeds, and disappears once the clutch is fully engaged. In this case the plate in question is the trapped disc, so you won't see it unless you dismantle the clutch assembly after removal.