As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AT CRUISE A VERY LOUD PULSATING ALARM SOUNDED THROUGH ALL CABIN AND GALLEY SPEAKERS. STARTED TO SMELL AN ODOR AFTER 30 MIN PRIOR TO LANDING. THE LOUD NOISE STAYED CONSTANT UNTIL SHUTTING DOWN THE AIRCRAFT. PERFORMED OPS TEST OF THE CABIN MANAGEMENT SYSTEM. OPS CHECKED GOOD IAW SMM 44-10-00-710-801.