I would imagine it has to do with your seering lock, aka your endpoint. If your end point is not adjusted right (too far), you put stress on the servo by throwing it too far and binding against some sort of piece on your model. A lot of servos will buzz, (or in the case of savox) buzz louder.
Most of the time this happens when you set everything straight, and then when you get on the track you adjust your trim, then that throws your endpoint off again.