I have a servo on a pull-pull set-up. With the clevis' disconnected from the rudder, everything is fine. Connect them and the servo jiggles back and forth. I tried increasing and decreasing the tension...no change. Pull the arm off and the servo is steady. Put the arm and steady. Connect the wires and leave them loose, fine. Attach to cnotrol horns (even loose) and it jiggles.

????