Thats pretty cool that he has the same name.. I replaced the motor because the crank and rod were ruined because of the spun bearing. I need to back up on it though, the more I think of it, it was quiet at an idle and knocked when I reved it up. I listened to your video again and it's hard to tell, but if it's a fast knock it can be something like a spun rod or wrist pin loose. That's because it will knock once going up and knock again when it changes direction going down. My brother in law had a motor that was knocking like a spun rod once and it ended up being the distributor cap was cracked causing pre detonation on one cyl. I had a knock on a motor that ended up being carbon build up on too of a piston smacking the head, just a few more ideas for you. I think if I were you I would drain the oil in a clean pan and let it sit overnight and check if any glitter settled to the bottom, also cut your filter apart and loo for any metal in it.