Make sure to seal the control surface gaps. One side only, use either covering material or simple tape.

The servos alone will not cause the flutter, although sloppy linkages can permit its amplitude to get out of hand.

Flutter is caused by rapidly changing pressure differential at the control surface. Sometimes turbulent airflow at the TE or seperated airflow will cause this. More commonly, odd airflow through a control surface gap can cause this condition. Airspeed plays into this, as the speed determines the pressure differential between the upper and lower surface of the wing (in otherwords, lift).

Having good servos will permit you to survive this condition, but it won't prevent it.

There is no racing, aerobatic or speed aircraft I fly which does not have each control gap sealed. It avoids this condition, ensures that the control authority at each elevator/aileron is the same as for the opposite side, and and also results in increased control surface authority (requiring less throw to achive the same aircraft response).

Bob