I had a rattle noise at mid to high RPM. Tried fixing other parts like the cam chain, tensioner, etc. and it didn't go away. Put my old cylinder back on and noise is gone. Piston slap? wrist pin? don't think so but don't know. Haven't narrowed it down to new cylinder, cylinder head, head cover, rockers or what. I'd like to return it since I'll just run my old parts to they're dead. Was just looking for a refresh but the kids want to ride and I don't want to trouble shoot.