I'll second (third? fourth?) the flutter deal, probably on the ailerons. The torquerod holes in my Avistar wing have gotten a little "widened" out by the rod and there is some pretty decent play in there, might be the same as yours. Are your aileron hinge-gaps sealed? Easy to do: Run a 1-inch wide string of white monocote all along the hinge gap on the bottom (have the aileron full up when you put it on to make sure you dont cause binding). Adds a little damping and safety to the ailerons.