I guess my approach would be to run it at the speed it rattles at, and push down/lift up/push sideways, everything related to the tank and tank support bracket. If nothing becomes obvious, next step would be to remove the flywheel and check to see if the coil laminations are hitting the rotating magnet in the flywheel. If you don’t know whether any wear marks are old or new, color the ends of the laminations with magic marker, then run it an reinspect. Lastly, if I had a spare lower unit, I would run the motor with that and see if the noise goes away. Strange as it sounds, problems with gear teeth can sometimes telegraph up and sound like they’re coming from the top end.
Long live American manufacturing!
