I have to dissagree with the comment above that sealing the hinge gaps eliminate flutter. Actually, sealing the gap has little or nothing to do with eliminating flutter. Unfortunately EVERYTHING WILL FLUTTER given the proper stimulus. The most common causes in models is 1:sloppy or limp (undersized) control push rods 2
versized holes in the horns (Zbends commonly have this problem)3:flexible surfaces (keep the surfaces as stiff as possible, i.e. no soft wood or easily flexed control surfaces) or 4; excess play in any part of the system. Even a wing that easily distorts or flexes can cause a stiff aileron to flutter. Often, the place you mount the horn to the moveable surface can minimize the onset of flutter. Never put the horn at 50% of the span on ailerons, always offset it to about 30 or 70% of the span if you can.