B767 PAX RPTS HEARING A BEEPING SOUND IN THE VICINITY OF HIS SEAT. CAPT ELECTS TO PROCEED WITH FLT. AFTER LNDG; NOISE IS DETERMINED TO BE CAUSED BY THE ACFT'S ROTATING BEACON.

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I RECEIVED A CALL FROM THE #1 FLT ATTENDANT. SHE TOLD ME THAT A PAX WAS CONCERNED WITH A BEEPING NOISE HE WAS HEARING IN THE OVERHEAD ABOVE SEAT XX. I ASKED HER TO INVESTIGATE. SHE RPTED BACK TO ME THE FOLLOWING: THERE WAS IN FACT A BEEPING NOISE COMING FROM THE OVERHEAD. AFTER A CURSORY EXAMINATION; SHE COULD NOT DETERMINE THE SOURCE; OTHER THAN IT WAS COMING FROM ABOVE. THE NOISE COULD BE HEARD ONLY WITHIN A ROW OR TWO OF ROW 10. THE NOISE WAS INAUDIBLE FURTHER AFT (OR FORWARD). THE GENTLEMAN WHO RPTED THE NOISE WAS THE ONLY PAX WHO WAS CONCERNED. IN ADDITION TO THE #1 FLT ATTENDANT'S RPT AND MEL GUIDANCE; I ALSO HAD AVAILABLE TO ME THE FOLLOWING INFO: THE FLT DISPATCH RELEASE ACKNOWLEDGEMENT DID NOT INDICATE ANY HEIGHTENED SECURITY CONCERNS. ALL FLT DECK INDICATIONS WERE NORMAL. I HAD NO EVIDENCE OF ANY SYS MALFUNCTIONS. THERE WERE NO ODORS; NO SMELLS; NOTHING. ALL FLT CTLS OPERATED NORMALLY DURING THE FLT CTL CHKS ON TAXI OUT. UPON OUR ARR; I HAD MY FO CONTACT MAINT TO MEET US AT THE GATE. I HAD NOT MADE ANY ENTRY INTO THE ACFT LOGBOOK; BECAUSE UP TO THIS POINT I DID NOT HAVE SUFFICIENT EVIDENCE FROM WHICH TO CONCLUDE THAT THERE WAS ANY MALFUNCTION TO WRITE UP. FO WENT BACK TO ROW 10 AND NOTICED THAT THERE WAS NO LONGER ANY SOUND. PUTTING TWO AND TWO TOGETHER; WE TURNED THE BEACON BACK ON. THE SOUND RETURNED. THE MECH HAD IN THE MEANTIME ARRIVED. HE RPTED THAT THE BEACON PWR SUPPLY WAS THE SOURCE OF THE NOISE.