Well, I removed it today. It all looked fine. No metal shavings. Felt
free with no binding. Gave it a close inspection and re-installed it.
Noise gone....beats me.

Bob Mears
Supermarine Spitfire

Hi Bob;

Did you happen to notice/measure wear on the oil pump rotor or the
oil pump mating face of the front iron?
I apparently managed to install one incorrectly once.  There was a
binding of some kind.  It would turn (by hand) with more effort than it
should.  I recall muttering a few four letter expletives,  pulled it off and
re-installed it.  Problem gone.  I assumed I had some minor shaft
misalignment.
(should I mention the 1 hour trying to get the shaft key back in properly?)

Cheers
Cary

He is talking about the Oil Metering Pump (OMP) Cary. Not the engine oil pump.