As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
LEFT ENGINE RUMBLING NOISE AT LOW POWER FELT AND HEARD. SEEMS TO SMOOTH OUT AT HIGHER POWER SETTINGS. N1 VIB IND 1.1. FOLLOWS THROTTLE MOVEMENT. ACOMPLISHED BORESCOPE INSP IAW MM 72-00-00. CHECKED ALL CHIP DETECTORS, NO DEFECT FOUND. RAN THE ENGINE IAW JRH 2-2-1, OK.