In most cases, the speed only aggravates another existing problem. It isn't the problem without another contributing factor, like slop in the linkage, uneven control surface alignment, or structural weakness that sets up vibrations. I had a Major Hobbies Fantasy that had chronic problems with elevator flutter. Skyshark RC took over the kit and redesigned the rear of the fuselage to stop flutter. The owner listed the changes somewhere here on RCU.

The original Funtana problems were related to too little structure in the wings. I think they added an extra rib near the servo to help. It wasn't flutter. The wings would break off.