[Graeme P]

I went through a similar mind numbing exersize trying to find a rattle ,replacing everything that moved adjusted rocker clearance twice replaced cam chain tensioner ,adjusted rocker side movement etc.
Finally seconds before I smashed the heads off with an axe I touched the left side plug cover and found it was jumping up and down in time with the noise I pushed on the cover and the noise stopped .
On close examination the plug wasn't loose in the head but the ceramic was loose in the metal body ,when it warmed up it would get looser and jump in and out.
Reaclling when the noise started I had to stop rather quick in traffic then checking out the blond in the car beside me I neglected to change back to first susequently stalling in 2nd or 3rd gear ,sounds rediculouse but it must have over pressurised the plug and loosened the crimp on the ceramic isolator and click click click.
Good luck with yours.