I had a flying buddy of mine look at my plane. he said everything looks good. I took up the extra and the clanking sound immediately echoed the flying field. he said it could be running too rich. brought her back down. placed her on the bench. we ran up the engine and we can hear the clanking sound. the rubber dubro exhaust deflector was vibrating around crazy but that wasn't it. the top of the cowl is secured but I don't have screws securing the bottom - the cowl vibrated but wasn't making the clanking sound. The cowl was making a lot of the high pitch vibrations thou. My buddy first tached the engine. at full throttle I was getting 9200RPM. he said the engine is capable of going faster - that I should get it closer to peak - maybe the engine is just running too rich. we got it up to 11000 and backed it up to 10500. stopped the engine and checked where the needle ended. I was a little frightened - the high needle ended at around quarter turn open from closed. I flew the plane again at the leaner setting but still heard clanking. Not as much - but was still there.