I'm working on my 1951 Chevy dump truck that has a PTO problem... I think. The truck has an sm420 and a Chelsea PTO with an idler gear that turns all the time the countershaft turns. The problem is as soon as the clutch is let out a grinding noise starts. I put in a rebuilt transmission, no better. I put new bearings in the PTO,no better. I took the PTO off ran the truck and the noise is gone. I checked that the PTO was correct and it doesn't have any obvious bad wear patterns. I used an extra gasket to increase backlash and the noise is the same. The noise is loud enough I don't want to drive it, anyone ever dealt with something like this before?