what airtronics servo do you have? if its a digital model, they do have sort of a humming sound all the time, some louder than others.. as for re-centering problems, welcome to the wonderful world of airtronics, lol! i have airtronics servos also. that used to be all i would run.. but theyre not as good as they used to be for some reason? ill be switching to JR or futaba soon enough...