Those ptos' will do that when the bearing is starting to go. I am thinking it is like a front clutch.
The gap should be adjustable.
My SIL give the front clutch pure h~((, reverse causes the clutch to stop, he reengages at full throttle, L O T S !!
That unit is smooth, at least it was when we replaced the bearing.
I guess if your rear pto ran a tiller, it would do well with a slight resurfacing of the plates.