Re: Kubota rattle
OP says filter was / is clean; I'd look at the pump, and check the air filter and supply.
Depends on what is making the rattle, I doubt it's valves. Could be related to the 'starve' i.e., mounts, gen head, belts binding and or slapping.
Jerry, you've got to stick your head in there and really eyeball the whole thing and see if anything is moving that shouldn't, or shouldn't and is.
Is the rattle in sync with the rpm?
Lessons learned are opportunities earned.