CK20HST PTO noise

I took a CK20HST for a test drive the other day and was quite impressed, started good, ran well, seems like a solid tractor. Only thing they don't have is a front mounted snowblower at this point.
The one thing I did notice is that when you used the PTO you need to use the clutch to engage it, you cannot just move the lever into the required position. When I disengaged the rear PTO (using the clutch) there was a chattering noise, so I rengaged and disnegaged a second time and still the same noise. Has anyone else noticed that.
MBT

Its probably an overrunning pto clutch. This keeps the PTO from forcing the engine to turn if it starts moving faster. In newer design tractors you usually can't hear that, but in the less refined models its not uncommon.