[amazondean]

I don't think the friction plate will be down to the metal, otherwise you would feel the clutch slipping. I am trying to rack my brains as to what it is. I could hear the engine noise in the background from your utube video as it was revving. This didn't seem to alter the noise of the rattle when revving, so that is why I was thinking the clutch release bearing. It does seem to point to the gearbox of some description, but those gearboxes are near bullet proof!