Very good and pertinent points Squid. Flutter is a very complex subject because its cause and effects are so very varried and is hard to comprehend unless you spend many hours in the study and measurements of cause and effect. Someones comments above on the fact that the main surface could be the origin of flutter is also correct; i.e. wing design could be the cause of what is perceived to be aileron flutter. With out extensive measurements on any individual case, it would be very difficult to pinpoint the exact cause. As to the comment of "Why do full scale designers mass counter balance some surfaces?", the reason is to make it physically less demanding on the pilot. Ailerons tend to droop and elevators also if not counter balanced requireing in some case excessive stick force to overcome at low speeds. It also releives shock loads on the control linkage durring high G forces. And, yes the fact still remains the Mass Balance does nothing directly to eliminate or minimize flutter.