As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
PILOTS REPORTED A VIBRATION IN THE LEFT ENGINE AFTER TAKEOFF. THEY RETURNED TO THE AIRPORT WITH NO FURTHER PROBLEM. INSPECTION REVEALED THE LT STARTER/GENERATOR ANTI-DRIVE END BEARING WAS BEGINNING TO FAIL. THE GENERATOR WAS STILL OPERATING; HOWEVER, PIECES OF THE BEARING CAGE WERE FOUND UPON REMOVAL INDICATING IMMINENT CATASTROPHIC FAILURE.