This weekend I'll pull the engine out and stick it back on the bench. I will also put in the canopy screws and see if that will solve the problem - actually, I'll try running the engine again on the plane with the canopy off. Oh, I wonder if it is the fuel plug knocking on the fuel tank or canopy. I moved the tank towards CG and have the fueling line strapped under the velcro thats holding the tank down. I'll test it this weekend.