Sometimes you may have to massage a servo hole and move the servo a little. Other times you may have to ditch the pushrods and run new ones. I used to spend hours adjusting and moving control surfaces to get things loose enough to eliminate a buzzing servo. One thing to keep in mind that when the engine is running, the vibration from the enigne may jiggle things slightly so that the servo centers and then does not drain out the battery. Sometimes you may have to be very creative to get at some places in the plane that you normally cant get to. Good Luck and don't give up