Since I have now solved my vibration and cracking-exhaust issue on my 912ULS Sting Sport, there is something I would add: Check your prop pitch very, very carefully. I am talking about both the pitch itself, and the synchronicity among blades. Changing my prop to a slightly higher pitch and carefully synching the three blades with a home-built laser device eliminated periodic and spontaneous high-pitch propeller resonnance--the root of all my troubles. I am flying smooth and happy again!--RD
