SleepyC
150cc
Vibration can cause this, ALSO, this is one that I would have never guessed but I had it happen. If you cinch down a servo lead too tight with a zip tie, it can cause weird things to happen. Like the wires crack under the zip tie, and it doesn't cause a short, but creates resistance that can make a servo act weird as hell, and it get's worse when the engine is running sending vibration through the airframe. Before ripping everything out, I'd try new servo leads as well.