Just to help dispel the rumor...

Having a gap has nothing to do with flutter.

Neither does the type of hinge you use.

EVERYTHING in the world has a frequency at which it wants to vibrate. If the turbulant airflow around your control surface reaches the right frequency, the control surface will try to vibrate.

The best cure is good, strong servos and no slop in the linkage.

If flutter continues, you have several options:

You can change the frequency of the turbulence by either sealing an open gap, or opening a sealed gap. You can also add vortex generators to your wing like the commercial airliners do.

OR

You can change the frequency at which the surface wants to vibrate by adding a weight to it.

But keep in mind that either of these cures will still not STOP flutter, they will just allow it to happen at a different speed - the trick is to have it happen at a speed at which you don't fly.