Lon,
When you pulled the cam cover back off to inspect the top end, did you notice if the banjo bolts still had their heads? Just a thought (a scary one at that). I still have no idea what would have caused the noise. I was thinking maybe if a banjo bolt head came off it could have sounded like that. But (1) I would expect serious damage would have occurred and would be very visible, (2) A bolt head would break off during installation not later.
Well a local independent mechanic (works on old BSA's, Triumphs, BMW, Norton, etc) recommended leaving it alone since it's running perfectly.
j
