Sam the Meat Man,
I think more 'descriptors' would be helpful. Is your clatter a dull heavy noise like a internal engine noise, or a tinny, sheetmetal, driveshaft clatter? Can you feel it as a vibration in your feet, seat or hands.
Have you discovered how to make it happen at will, and can you do this only when moving, or just sitting still or both...under load or coasting..low RPM or high RPM or is in not related to the engine, but more to the drive train...lots of research left to do.
Stuart
