Yes, I have already replaced the oil filter checkvalve. Unfortunately it made no difference in my case.
However, removing the oil pump relief valve and then reinstalling it (after I determined that the replacement part would not fit in my oil pump) solved the problem (at least for several weeks).
While it did return, it has now dissappeared again.
I detailed in a previous thread somewhere all that I have done so far, but in summary it entails timing chains, tensioner, oil filter checkvalve, and then finally my attempt to change out the oil pump relief valve.
I'll keep everyone posted on the saga as it continues. In the interim, I just keep driving.
Keep up the revs.