What was found
ABOVE 15,000 FT THE AIRPLANE BEGAN TO SHAKE. AUTOPILOT, TURBULENCE, ENGINES, AND SPOILERS WERE ELIMINATED AS FACTORS. APPLYING EITHER RT OR LT RUDDER PRESSURE STOPPED THE SHAKING. IDENTICAL SYMPTOMS IN 2 PRIOR INSTANCES PROVED TO BE RUDDER FLUTTER DUE TO ACTUATOR ROD END BEARING WEAR. COMPLETED INSTALLATION OF YELLOW, GREEN, AND BLUE SYSTEM RUDDER ACTUATORS REF AMM 27-24-11-04. PERFORMED ADJ/TEST REF AMM 27-24-11-04.OPS CHECKED NORMAL. PERFORM RUDDER SERVO CONTROL JAMMING DETECTION REF AMM 27-24-12-04 OPS CHECKED NORMAL. SURFACE POSITION INDICATING ADJ/TEST CHECKED NORMAL REF AMM 27-25-00-05.