I have studied aerodynamics. And I didn't just state an opinion, I gave an explanation. You're the one who stated opinions with no explanations.

I explained that air flowing through a control surface gap can cause changes in air pressure above and below the control surface and that some times these changes in pressure can oscillate. This produces a force that tries to move the control surface back and forth with the oscillation. If it hits a resonant frequency and the control system isn't up to the challenge, this can help initiate aerodynamic flutter.

Now, please explain how a sealed surface can cause flutter instead of just stating YOUR opinion as fact. Then explain why an oscillating pressure wave on the control surface won't impart an oscillating moment on the surface.

Dave