I don't get any grinding on our CK35 - sometimes it might feel a little "stiff" or a quick bump when engaging.
Especially for Brush Hogging where it's trying to spin up all that mass, I engage at idle and very gently let out on the clutch till things get moving, then throttle up.
Not trying to be a smart @$$ but (I'm assuming you have the gear model and not the hydrostatic) you do know it's a 2 stage clutch and depressing part way only disengages the transmission. To fully disengage the PTO you have to depress the clutch ALL the way thru it's range of travel. I bring this up because it was new to me coming from the old 8N Ford where depressing the clutch disengaged both transmission & PTO together. From my "muscle memory" if I wasn't moving then the PTO wasn't turning either so I had a little learning curve.
Hopefully it's this (or maybe the clutch linkage has slipped / out of adjustment and you're not getting the second stage like you think you are) and not something more serious.