You are turning your transmitter on before the receiver right? Never turn on the Rx before the transmitter, you can damage the servos.

You might also have a little binding in the aileron(s) themselves, which could cause the servo to "chatter". Chattering is usually the servo trying to center itself, and if there's binding anywhaere it will never quite center. (Broken tooth will also cause it, but you looked already.)

Good luck,
Dennis-