RC,

Just to be clear, if your servo arm and flap control horn are in-line and the servo arm is moving in that same plane (ideally, 90 degrees to the flap hinge line) then the ball end is not really necessary and may actually not be desirable. With the ball end mounted to one side of the control horn and/or servo arm, a twisting moment is created on the horn/arm, making the linkage less solid.

If the servo arm and control horn are not reasonably in alignment, then the ball link is an acceptable solution to resolve the geometry mismatch and potential load on the servo.

My best guess is that your servo buzz is just the resistance of the flap seating in the full retract position and not necessarily a linkage problem. The current meter will tell the story and it may be an acceptable draw or else just a click or two of throw off full up to minimize the draw/buzz.

Craig