As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING CLIMB AT FL400, THE AURAL FIRE WARNING HORN SOUNDED. THERE WAS NO SIGN OF FIRE OR SMOKE IN THE CABIN AND NO LIGHTS ASSOCIATED WITH THE WARNING HORN. AN EMERGENCY WAS DECLARED AND AIRCRAFT RETURNED TO CUN AND LANDED WITHOUT INCIDENT. CLEANED AND RESEATED AURAL WARNING HORN CIRCUIT CARD. OPERATIONAL CHECK NORMAL.