Not meaning to be a wet blanket, but what you have done is add your mass to control surface, which invariably leads to more overshoot when stopping and tends to increase the chance of the control surface oscillating. Static balance of the control surface has practically nothing to do with whether it will be prone to flutter in flight.

BTW, your original concern of the servo buzzing at neutral is normal with digital servos. I'm not familiar with the Futaba 3010, but if it is digital and buzzing a little all the time, it's doing what it's meant to do. Birds gotta fly, bees gotta buzz and so do digital servos. Lose the counterweights and go fly!