The ol’ loose flywheel syndrome. I have experienced that and took me way too long to figure out what the noise was. But now I know and I can tell you that if your flywheel is loose, you will only notice/hear it at idle when the motor is loping (the cranks angular velocity is rapidly increasing and decreasing causing the flywheel to slam from side to side on the bolts, thus causing the knock). When you accelerate the motor (in neutral) of course the flywheel is pressed up against bolts and your noise goes away. Rod knocks only get louder as RPMs increase, flywheels get quieter.

Sounds like it is time pull the pan and get dirty. If you spun a bearing you will most likely see the blue rod cap immediately.

Funny how that works huh! It is always the day after the warranty expires or right after you pay cash for something, that it breaks!

Keep us posted

Brian