The jiggling servo or is it servos ? If only the 1. It may be a tight spot in the stabilizers travel. If it is ALWAYS in the same angle, it is a bind. Remove it somehow. You can have SEVERAL binds on ANY moving surface. Your hinges should allow the surface to move easily with a gentile puff of your breath.
I hope you DO NOT have ANY metal to metal linkages. Like a metal adjustable clevis to a metal control horn. OR loose bolts & nuts. They can cause small to very wild servo movements. DO NOT test the controls of any plane indoors. Metal beams, roofing, or siding will sometimes cause erattic servo & or motor operation. I have had ESC's go from stopped to any amount of speed the reflections inside the building could create. 1 plane almost got me in the belly......Outside only.

Sorry if you know all this already. Tell me so I do not keep going on. I do not know your abilites.