What was found
DURING CRUISE FLIGHT AT FL390 WITH CLEAR AIR AND SMOOTH RIDE , WE FELT A MOMENTARY UNCOMMANDED BACK AND FORTH YAWING MOTION. SUBSEQUENTLY AT FL350 WE AGAIN FELT A MOMENTARY UNCOMMANDED BACK AND FORTH YAWING MOTION. THIRDLY AT FL310 WE FELT AND OBSERVED AN UNCOMMANDED RIGHT RUDDER APPLICATION FOR APPROXIMATELY 5 SECONDS , WE FELT THE AIRCRAFT YAW AND OBSERVED THE SLIP AND SKID INDICATOR MOVE ABOUT HALF SCALE TO THE LEFT. THE CONDITION THEN CORRECTED TO NORMAL. THE AUTOPILOT WAS ENGAGED DURING ALL 3 EVENTS. DIVERTED TO IAD FOR A NORMAL LANDING. NO OTHER UNCOMMANDED RUDDER INPUTS OBSERVED. R & R RUDDER SERVO FELT A MOMENTARY UNCOMMANDED BACK & FORTH YAWING REF AMM 22-11-01. OPS CHECK OF RUDDER SERVO GOOD.