It’s a little bit unusual to have flutter and survive, especially on an airplane built as lightly as ours. Some of the high performance servos tend to jitter after they get a bit of use and I have seen that mistaken as flutter on more then one occasion. That said, let’s dive into a few particulars. The first thing that I would like to know is your control horn length from hinge point to ball length. Then your servo arm from output shaft to ball link. Next is servo arm material?The servo brand and model number? What battery voltage and capacity? What brand of switch? How many voltage input connectors into the receiver. A bit of a lengthy list but all these items and a few more things do play a part in solving your issue.