Mine started to make a rattle at 25 hrs , found left power valve retaining bolt missing and power valve assembly had been vibrating horizontally and vertically in the barrel and slogged the hole to egg shape slightly , I put a bolt in but didn't stop the rattling , pull your powervalve covers...
Did you have a lean spot at around 1/3 to 1/2 throttle ? I have dropped clip to bottom position nearly got rid of it but not quite , have tried various needles but still end with pinking