Hi all, recently bought a 2002 Ktm 520exc. When I inspected the bike everything was in great order. Took the bike for a few quick rides and all was still great. adjusted the valves and changed the oil (including filters...used good Motul 300V 10-40w). I took the bike for a spin and everything was ok. The bike sat for a few hours and when I restarted it, I heard a horrible knock from the bottom end. Hold in the clutch and it disappears. From reading online I figured it might be the primary nut on crank. I checked that and all seemed tight. pulled the clutch plates out and nut on basket was tight and no play in clutch at all that I can see. Everything else seems good...... Any ideas? is it a bottom end rebuild?