[Evgeni]

Thanks Day Mow - put some 15w50 in tonight. Goodbye engine vibrations! The knock is still there, but you need to stick your head in the wheel arch to hear it when the motor is warm. Not losing power, so the jury is out as to whether it is an issue with the bottom half. Idle has smoothed out as well.
Maybe the oil I had in before accummulated too much water with all the rain that we have had. No metal glitter in the oil that came out either.