Sounds like a bolt has backed out of the clutch and is rubbing against gear teeth. Loud vibration/knocking noise when in gear and clutch is out. Tractor moves but it does not sound like a good idea. Quiet when in neutral. Years ago a bolt did back out of the clutch and it would not release (or so I was told). I suspect I will need to have it loaded on a trailer and taken into a shop, have the case split, etc. That kind of repair is beyond my skills/tools/time. Is that worth it on a '56 200, which is worth only $1,500 max anyway? I could buy, for instance a 1975 Farmall 574 for $6,600 with a bunch of accessories - seeder, bush hog, rear blade, front bucket. I could use the extra hp as well. Is that a good model? The 200 is the only tractor I have used.