What was found
TAIL VIBRATION, RTFL. CLIMBING THRU FL310 .75M FELT MODERATE TAIL VIBRATION. SLOWED TO .7M VIBRATION WAS LESS BUT DIDN'T DISAPPEAR. INCREASED SPEED BACK TO .75M VIBRATION RETURNED. REDUCED SPEED TO 250 KIAS FOR RETURN TO DEPARTURE. VIBRATION VERIFIED BY CREW IN AFT CABIN. ACP REVIEW OF VIBRATION SURVEY FOUND RUDDER AND ELEV WITH HIGHEST SCORE. CHECKED PLAY AND RIG OF ALL FOUR ELEVATOR SERVOS. ALL GOOD. FOUND ALL THREE RUDDER ROD END PLAY CHECKS OUT OF LIMITS.