Hi guys. I had a model that flew great until I cut out a new wing and installed it. It had much the same problem, I got flutter in a high spead dive. I repaired the crash damage, looked for problems, nothing loose, no hinge gaps. I sealed the hinge surfaces. I crashed again. I consulted my club members, and found the wing airfoil was just a little bit thicker than the old wing. The consensus was I was flying too fast for the airfoil, causing the air to seperate from the surface. That creates turbulance that reaches the control surfaces and causes flutter. There is no fix other than to slow down, or build a wing with a thinner profile. Its called overflying your wing ! I just put a bigger diameter prop with less pitch on. The model flew better manuvers and landed slower. I was a happy man. Speed is not everything. I looked at the pics of your plane and it looks like a pretty thick airfoil. The engines that were around when that plane was designed, didnt put out the power that the modern day engines do. You might consider the prop fix. Happy flying!