aubiecat,
Instead of guessing and playing around with this and that you need to take a logical approach to find the problem. First of all disconnect the pushrods from the servo and see if it still buzzes. If not then the problem is in your linkage or the control surface. If it does still buzz that you have a servo going bad (if this is a non-digital servo it shouldn't buzz at all in the neutral position). Next, reconnect the pushrod to the servo. If it buzzes while it's in the neutral position then there is something about the control surface that is pushing back against the servo, you need to troubleshoot the control surface so that it naturally sits in the center position. Move the servo from side to side. If the servo moves to the end of it's travel and then buzzes the problem is that the servo is trying to push the control surface farther than it can physically travel. You need to reduce the amount of travel that the surface can move. You can do this by adjusting the position of the control rod on either the servo arm or at the control surface. At the servo arm you can move the control rod to inside holes to get less travel, at the control surface move to the outside of the arm for less travel. Adjust the position of the control arm so that you have less throw and this should remove the buzzing when the servo is at the outside range of it's motion.

It was mentioned above that a little buzzing was ok, this is not correct. If these are non-digital servos they should not buzz. The buzzing is caused by either something pushing against the servo when it's centered or by the servo trying to push farther than physically possible. Both of these situations are bad. First off they cause the servo to draw more current from you battery, which will drain your battery quicker. Also, pushing against the limit of travel can damage your servo, your pushrods, or your control surface. Please take the time to troubleshoot the problem and correct it.

Hope this helps

Ken