I've bought a used pattern plane with 9202 servos on rudder and elevator.

Both servos make often make a loud hum when moving the control surface.

I'm not familiar with this servo. It seems to work OK, but the sound makes me nervous. Any one here have some experience with these and can comment?

I see you can buy new gears for the servos but am not sure if that is their problem.

TIA for any advice.