Could be a number of things, but, I had a wheel bearing fail which acted that way, it was the rear wheel sprocket bearing. It's symtoms were: 1) a "ballsy rumble" noise when the bike on the centerstand and wheel spun, 2) The rear wheel drive spocket had side to side play of about 1/8th inch.
Other things it could be: rear wheel lock nut is loose and tire rubbing on chain stay, or rear wheel out of alignment, or broken brake return spring activating one shoe.
If the clutch has the innermost plate inserted the wrong way, the ball bearings in the clutch basket will pop out and start bouncing around the primary chain case (ask me how I know).