First, thanks to everyone for help with the 3pth pivot bolt replacement. All went well. This is an old problem that I should have investigated when the oil was drained but needed the tractor for a bit. The tractor has a two stage clutch. When I engage the PTO with an implement attached (snowblower, brush hog or tiller) the PTO chatters for a second or two and then smooths out. Another thing I noticed is that when I raise the 3PTH with a heavy load (bucket with gravel), I hear a knocking sound. Do I have a bad bearing in the PTO drive chain? Is the clutch going bad? Is the hydraulic pump weak? Are the two symptoms related? I know the clutch is weak. It tends to grind when I put it in gear to drive. It doesn't grind when I put the hi-neutral-lo selector in neutral first. I have some trouble engaging the PTO selector lever. I don't have the know-how to swap out a clutch. Is there something I can check before I float it to the shop or look for a local roving mechanic?