Metal gears expand once the servo warms up, many manufactures set the mesh so tight cold they tighten in use, poor centering or high current use is the result. I use exclusively JR servos in 100% of my jets and large models. Never seen flutter on any model, never will due to gear back lash. Mechanical set up on linkages has way more influence. Many of the worlds best pilots use JR servos, there is good reason.