I hate to disagree with Mr. Buckner as he is most often right on when it comes to a solution to a problem; but, mass balancing will not necessarily cure any flutter. Perfectly balanced systems can and do oscillate or flutter if given the impulse or input to generate the frequency at which they are resonant and mass balancing a surface that will flex or maintain oscillation does nothing to cure that. I'm a firm believer in mass balance, especially on elevators and ailerons but not for the reason that it prevents flutter.