RE: Questions regarding Flutter
First off - My advice is Do Not fly the plane until you solve the flutter. If you really have to - keep it slow and away from the speed where the flutter occurs.
I have seen flutter tear a plane apart in mid air in a couple of seconds. (U-Can-Do60 using the standard control gear that came with it - being flown fast). the control surface basically vibrates at such a frequency and force that it simply shakes the plane apart. The pilot has no control over the plane while that occurs and it has the possibility to put people in danger.
It is difficult to find exactly where the flutter is without observing the flutter. I wouldn't recommend making it flutter on purpose. Just look closely at all the control surfaces. For any of the conditions below.
There are a lot of things that will contribute to flutter.
A wide hinge gap - that can contibute - taping them will help but if they are too wide anyway, it is better to fix that problem first - then tape the gap.
Slop in the control linkages - Clevises, ball joints, z-bends through oversized holes in servo arms will all contribute to this - make suere there is no excessive slop in the connection between the control surface and the servo motor (That includes the servo gear train).
Weak Servos - are they adequate for the job?
Flying a plane with large control surfaces or throws too fast. That will exacerbate any of the issues noted above.