My bike and one that MSSpring had both had a horrible rattle from a loose flywheel nut.  Since the flywheel is on the end of the crank and the rattle sound goes into the crank bearings and rod....it resonates from the engine block and cylinder.  It doesn't sound like a top end rattle, it sounds more like a cylinder noise.  It starts out as a tick and gradually works into being a loud hammer noise at idle.  The sound is loudest at idle and gradually gets softer as the revs increase.

So my motor is eating itself.

What year motors should I look for that is compatible with 2001.  Don't want to have to replace any harnesses if at all possible.