A B767-300 IN A DSCNT INTO A HOLDING PATTERN WITH OTHER ACFT; HAD EICAS WARNING WITH A LOUD SIREN. SIREN BLOCKED OUT AIR TFC COMMUNICATION.

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SBGR WAS BELOW LNDG MINIMUMS. WE HAD JUST BEEN GIVEN HOLDING INSTRUCTIONS TO A FIX NOT ON THE FLT PLAN. FLT CONDITIONS WERE SMOOTH IN LEVEL FLT. NO CHANGES TO ANY FLT CTLS WERE BEING MADE. SUDDENLY; THE 'FLAP' WARNING LIGHT ILLUMINATED ON THE EICAS; AND 'AIR/GND DISAGREE' STATUS MESSAGE ALSO APPEARED; AND A VERY LOUD SIREN WHICH COULD NOT BE SILENCED. WE WERE UNABLE TO HEAR ATC BECAUSE OF THE VOLUME OF THE SIREN. THIS WAS MOST TROUBLING BECAUSE WE WERE SOON TO BE GIVEN DSCNT INTO AN AREA WHERE SEVERAL OTHER AIRPLANES WERE ALREADY HOLDING. WE TRIED SEVERAL METHODS TO SILENCE THE WARNING. ALL WERE UNSUCCESSFUL. WITH GREAT DIFFICULTY; WE PATCHED MAINT FOR HELP. THANK GOD THE WARNING STOPPED AFTER ABOUT 3 MINS; DUE TO NO ACTION OF OURS. MAINT THEN CONTACTED US AND GAVE US FOUR CIRCUIT BREAKERS TO BE PULLED IF THE WARNING OCCURRED AGAIN: B-16; B-18; H-35; AND J-34. FORTUNATELY; WE DID NOT NEED TO PULL THESE BREAKERS. I LOVE BOEING AIRPLANES; BUT I CANNOT POSSIBLY SEE WHY ANY MANUFACTURER WOULD BE ALLOWED TO SOUND A LOUD WARNING; WHICH COULD NOT BE EASILY SILENCED. IMAGINE WHAT MIGHT HAVE HAPPENED IF THIS WARNING HAD NOT STOPPED OR HAD SOUNDED A FEW MINUTES LATER. WE COULD HAVE BEEN IN DANGER OF A COLLISION WITH ANOTHER ACFT. OR CONSIDER THIS HAPPENING ON THE EXPECTED LOW-VISIBILITY APCH. PLEASE; PLEASE; ADD A QRH PROC FOR THIS EVENT AND PLACE COLLARS ON THESE FOUR CIRCUIT BREAKERS SO THAT THEY CAN BE EASILY LOCATED. IDEALLY; THERE SHOULD BE A SWITCH TO SILENCE ALL AURAL WARNINGS. I UNDERSTAND; HOWEVER; THAT A GND CONFIGURATION WARNING SUCH AS THIS ONE IS NOT DESIRED TO BE EASILY SILENCED. GREAT IDEA; EXCEPT WHEN IT OCCURS AIRBORNE! CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED THAT AFTER 3 MINUTES OF THE TKOF WARNING SIREN; IT STOPPED AND COMMUNICATION WAS RESTORED. DURING THREE MINUTES OF SIREN WARNING NOTHING COULD BE HEARD EVEN WITH THE CREW WEARING HEADSETS. THE CORRECTIVE ACTION TAKEN IS UNKNOWN AS MAINT HAS NOT RPTED. RPTR ALSO STATED THAT THERE IS NOTHING IN THE QRH FOR THIS TYPE OF EVENT.