Steve, is there an air conditionor on that thing?

And, not trying to call you out...but

Did you pop the hood, and verify where the noise was coming from, like with a mechanics stethoscope(screwdriver, peice of wood, etc)?

I am asking, becuase I have had problems in teh front accessories(pulies), bearing locking up, clutch in teh a/c compressor, etc, and caused me all kinda noises, and odd running.

Not touching the oil pump thing though, as I have yet to tear apart one of the isuzu 4 bangers.

But, usually, we prime the oil pump when an engine is re-assembled, and VERIFY it has pressure, before it is run for the first time...

Chase