Steve,
Buzzing can be either good or bad. If you have digital servos then the buzzing is normal. If you have analog servos then the buzzing is bad. Digitals are always moving to maintain center. This is a good thing, except it does cause them to drain batteries faster than analog servos. For analog servos its bad because you either have a bad potentiometer or you have something binding that is causing the servo to not return to center. Either way it's going to drain juice from your battery and it should be addressed.

Ken