I am not sure if you are describing an unusual servo condition or not. I am not exactly sure what you mean by "on". Your servos are "on" any time your receiver is turned on. However, when the flaps are up (neutral) you should not hear any buzz from the flap servos. When the flaps are up the servos should be at their neutral positions or, centers; eg. not turned in one direction or the other. If you hear a buzz from the servos it could mean that there is binding somewhere in the linkage or the flap itself. It could also mean the servo is defective. Hope this helps.

Brian