As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
(CAN) ON A REVENUE FLIGHT, DURING ACCELERATION TO TAKEOFF, THE PILOT HEARD A RUMBLING NOISE FROM THE LT ENGINE AND FELT THE VIBRATION. THE ACFT RETURNED TO THE HANGAR AND UNLOADED PASSENGERS. THE SAME SCENARIO WAS REPEATED ON A GROUND RUN. VISUAL INSPECTION DID NOT REVEAL ANYTHING ABNORMAL. TROUBLESHOOTING ONGOING.