Should we start a sweepstake?
I'm with valve train. The suspense is killing me. Pull the valve covers. :-)
Alan

My money is on badly set valve clearance!

Any news yet?

Diagnostic tool........
 

Use a mechanic's stethoscope to locate and isolate the offending noise. It could be any of the previously mentioned culprits. So you need to systematically identify the root source and cause of this problem. Keep us posted.

Tony

valves...I just did my own rebuild and I got the same sound...Mine settled after awhile and I readjusted the valves.

It was the fan blade rubbing. He figured it out.

Are you 'his' spokesman?

Really? I wouldn't necessarily have guessed that....surely they'd be witness marks in the yellow paintwork? (or are there? perhaps they're out of shot?)