As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
MIDDLE FREQUENCY VIBRATION FELT IN THE NR 1 THRUST LEVER AT ALL POWER SETTINGS ABOVE 1.4 EPR DURING FLIGHT. RETURNED TO DENVER. PERFORMED ENGINE VIBRATION SURVEY ON WING PER MM 72-00 TEST 1, ENGINE WITHIN MANUAL LIMITS. OK FOR CONT SERVICE.