I have an 07 660 rhino.
Mods are:
hunterworks tri-fire cdi
hunterworks machined sheave
E.P.I "orange" spring
custom 2" exhaust tip
carb work
SS108 and 26" swamp lites
Home made half doors w/ factory yamaha latches
After reading and searching for info on "clutching" on numerous sites...
I had the same noise and it was the primary sheave support cage bolts. two long bolts and two short ones. make sure they are in the correct hole and make sure they are tight