I have taken most of the plastic off so I can get at the engine. Using my experience with automobile engines, here is what I have done so far to try to determine the problem.
I took the plugs out and checked each cylinder for play in the rod bearings.
Cranked the engine by hand and got each piston on the down stroke, then pushed real hard from the top to see if I could find some play. I could not detect any play in the rod bearings.
I also pulled the plug wires one by one while the engine is running to see if the noise quit or got quieter. The engine slowed but the noise stays the same. I am beginning to think it is not a rod but rather something in the top end.
Any old timers familiar with motorcycle engine noises please listen to this and give me your opinions.
https://youtu.be/mec8aCRRl80