I think he meant centering/reSolution. It is possible that these problems can be caused by the transmitter, but more than likely the pot is worn in the digital servo. One thing I have heard of being done to stop this (and keep in mind this is just a temporary fix) is using the sub-trim in your transmitter to re-define what center is, and adjusting the servo arm accordingly. The digital servos are constantly searching for center, which can account for a certain degree of buzzing, but when it gets to where the control surface is being moved by this search for center, it's time to repair or replace.