grinding sound on nrg?

i got a piaggio nrg power dd with leo vince tt and i noticed it sounding rough and grinding all the time especially under hard acceleration where it sometimes revs to 10,000rpm so i took the side cover off and checked crank bearings and variator and rollers and they seem to fine as their is no freeplay in the bearings but i couldnt get the clutch off so unsure if that need replacing the only other thing that could be making all the grinding sounds is the gearbox bit is it much of a problem if gears grind or are they supposed to after a while if not how much would it cost to get all of it replaced(i checked the oil which is fine)could that be the cause my bike losing power wen throttle opened