Then that is pretty normal, the servo is just working against the load of the surface.

A consistent buzzing with the servo at center or at any point in it's travel is almost always friction and most likely occurs when the pushrod is either in a tube or making a slight or even not so slight curve or bend along it's length. It is also possible that the throw is set a little bit to much on the servo and the control surface is running out of throw before the servo gets to it's end point (flanked)


Montague has a great idea on checking...