ORIGINAL: jester_s1
That's a common myth that sealing the gaps prevents flutter. Sealing the gaps improves control authority and reduces drag so one should do it, but it doesn't prevent flutter. Flutter is caused by turbulence hitting the back edge of the control surface, which has nothing to do with the hinge gap.
Very true. However, the act of putting tape over the hinge line does tend to stiffen up the surface a tiny bit so that fact may change the flutter characteristics a bit (shifts the resonant frequency to a higher number) so that the stimulating energy may no longer be at the new resonant frequency giving one a false sense that closing the gap stopped the flutter.