I didnt know flutter had so many causes. Always thought that

If you had a thick airfoil and flew it too fast, the air flow would seperate over the tapering part of the foil (part after the main spar when the cross-section starts reducing). This would induce turbulence causing sudden high and low pressure pockets to form on the same side of the control surface. This would cause the surface to move exagerating any play in the linkages.

I also thought that aileron hinge gaps would allow air to "leak" from the higher pressure undersurface to the lower pressure upper surface and this crossing of flows would induce the flutter.

Is my understanding of the issue wrong?

Ameyam