As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
ON CLIMBOUT, HAD UNCOMMANDED RUDDER INPUTS. PERFORMED AIR TURN BACK, LANDED WITHOUT INCIDENT. FOUND UPPER RUDDER PULSATING IN BOTH DIRECTIONS FROM NEUTRAL. TURNED OFF UPPER YAW DAMPER, PULSATING STOPPED. DEFERRED SYSTEM PER MEL 22-6. UPON LANDING AT CVG, REPLACED YAW DAMPER COUPLER PER BOEING M/M 22-10-0.