As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
GEARBOX WAS OVERHAULED AND NEW GEARS WERE INSTALLED. STATIC PATTERNS ON GEARS MATCHED TESTER SHEET AS REQUIRED. AFTER A FLIGHT OF 15 MINUTES CREW HEARD A HIGH PITCH NOISE FROM GEARBOX. GEARBOX WAS DIASSEMBLED AND COULD NOT FIND ANY DISCREPANCIES. NOTICED THAT PINION GEAR HAD A ZF SERIAL NUMBER AND BEVEL GEAR HAD A M AS A PREFIX WHICH IS UNCOMMON, PLEASE EVALUATE.