G'day Mate,
It's actually control surface flutter, not a lot to do with servos, unless they are very weak, the control surface whether it is elevator, aileron or rudder, oscillates, back & forth, at a very high speed caused by many things, such as loose linkages, which can allow movement, or large gaps in the hinge line.
I have even had the experience of aileron flutter caused by a sloppy aileron torque rod, where it was positioned in the aileron, it allowed the aileron to move up & down at a very high frequency, when the plane was at full throttle, luckily I throttled back & slowed the plane & landed safely, but it can cause the destruction of the tail or wing very quickly, if allowed to continue.
And planes don't fly very well without a tail, or wing half.