The balancers (counterweights) are what I thought of, too. But if you only get flutter in a full-power dive you have a fine set-up already. Some models will tear themselves up at full throttle in straight & level flight (overpowered 3-D models, for instance). My Ultimates and my Hot Stik could shred control surfaces at full-power in level flight. Avoid full-powered dives. "Real" aircraft do.