As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
PILOT REPORTED AURAL WARNING IN HELMET. NO OTHER INDICATIONS ON ANY OTHER INSTRUMENT PANELS OR WARNING UNITS. THIS AURAL WARNING IS SIMILAR TO THE FIRE WARNING "GONG" HEARD WHEN COMPLETING THE SELF TEST DURING PREFLIGHT CHECKS. TECHNICIAN CONFIRMED AURAL WARNING DURING FUNCTIONAL CHECK. REMOVED AND REPLACED FAULTY DETECTOR AS REQUIRED. RETURNED TO SERVICE AFTER FUNCTION CHECKS COMPLETED.