FA ON A320 ACTIVATED THE CABIN/COCKPIT ACCESS CODE WHICH IS A NON CANCELABLE ALERT. THE ALERT WAS SO LOUD THE CREW WAS NOT ABLE TO HEAR RADIO XMISSIONS IN THEIR HEADSET. THEY HAD AN ALT DEV AS A RESULT.

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PER OUR FLT PLAN; REQUESTED CLB TO FL370. AFTER A BRIEF DELAY; SIMULTANEOUSLY; ATC CALLED WITH A CLB CLRNC AND OUR 'A' FLT FLIGHT ATTENDANT ACTIVATED THE CABIN COCKPIT ACCESS CODE TO ACCOMMODATE A RESTROOM BREAK AND TO DELIVER CREW MEALS. THE COCKPIT ACCESS AND THE FA CALL TO COCKPIT SYSTEMS ARE BOTH 'NON-CANCELABLE' ALERTS. STRUGGLING TO HEAR OUR ATC CLB CLRNC; BOTH PLTS THOUGHT THEY HEARD CLB TO FL370 AND WE REPLIED; 'ROGER; CLB AND MAINTAIN FL370.' FL370 WAS SET IN THE ALT WINDOW AND IT WAS CONFIRMED PER SOP. A CLB WAS INITIATED AND I; THE PNF; (CAPT) DEPARTED THE COCKPIT FOR THE RESTROOM. UPON MY RETURN; I WAS ADVISED THAT ATC HAD QUERIED OUR FLT AS IT NEARED FL360. FO REPLIED THAT WE HAD BEEN PREVIOUSLY CLRED TO FL370. ATC INDICATED THAT THEY THOUGHT WE HAD BEEN CLRED TO FL350. HOWEVER THERE HAD BEEN NO LOSS OF SEPARATION; WE WERE TO MAINTAIN OUR HDG AT MACH .73 AND CONTINUE OUR CLB TO FL370. SUGGESTED SOLUTIONS TO MITIGATE THIS ISSUE: 1. CONSIDER THE FACT THAT 'EVERY' EMER WARNING; BELL AND LIGHT IN THE COCKPIT CAN BE CANCELLED. EVERY EMER CHKLIST HAS AS ITS SECOND LISTED ITEM; BEHIND FLY THE AIRPLANE; 'SILENCE THE WARNING.' WE THE CREW; ARE FAMILIAR WITH THE DIFFERENCE BETWEEN A COCKPIT ACCESS AND A FLIGHT ATTENDANT CALL SYSTEM ALERT; PLEASE REMOVE THE NON-CANCELABLE ELEMENT OF THESE DEVICES. IMAGINE IF YOU WILL; THAT THERE HAS JUST BEEN A CATASTROPHIC FAILURE; THE PLTS ARE DOING THEIR BEST TO WRESTLE AND REGAIN CTL OF THE ACFT. THE PLTS ARE AWARE OF THE PROB! BUT FROM THREE OR MORE LOCATIONS IN THE ACFT; EVERY FLIGHT ATTENDANT JUST HAS TO BE SURE THAT WE KNOW WHAT'S HAPPENING. EVERY TIME THIS SYSTEM IS ACTIVATED; EVERY ELEMENT OF COMMUNICATION STOPS. THIS COULD WASTE VALUABLE TIME AND SERVE AS A MAJOR DISTRACTION. 2. IF THERE IS THE SLIGHTEST DISTRACTION; THE CREW SHOULD AUTOMATICALLY VERIFY THE CLRNC (PERIOD). FOR US; WE BOTH THOUGHT WE HEARD 'CLB AND MAINTAIN FL370.' MAYBE IT WAS WHAT WE WANTED TO HEAR AMIDST THE NEAR DEAFENING SOUNDS OF THE COCKPIT ACCESS SIGNAL. SUPPLEMENTAL INFO FROM ACN 629606: WE REQUESTED A CLB TO FL370 AND JUST AS OUR CLB WAS READ TO US BY ATC; THE CABIN CALL BUZZER SOUNDED LOUDLY. AS IT IS NOT POSSIBLE TO CANCEL THE BUZZER; WE WERE FORCED TO LISTEN TO IT FOR MANY SECONDS. THE CAPT AND I BOTH THOUGHT WE HEARD A CLRNC TO CLB TO FL370; AND THE CAPT READ BACK FL370. THE CAPT SET FL370 IN THE ALT WINDOW AND I PULLED THE KNOB FOR OPN CLB. WE BOTH POINTED AND RECITED '370.' THE FLIGHT ATTENDANT ASKED IF WE NEEDED A LAV BREAK AND I TOLD HER WE DID. AFTER PROPER SECURITY PROCS WERE COMPLIED WITH; THE CAPT LEFT THE COCKPIT. WHILE THE CAPT WAS IN THE LAV AND WE WERE CLBING THROUGH FL360; ATC NOTIFIED ME THAT WE WERE ONLY CLRED TO FL350. I ACKNOWLEDGED THE CALL; AND RESET FL350; AND INITIATED A DESCENT TO FL350. JUST AFTER WE STARTED THE DESCENT; ATC CLRED US TO CLB TO FL370; SO I RESET FL370 IN THE ALT WINDOW AND INITIATED A CLB. THERE WAS NO REDUCED SEPARATION ISSUE. WHEN THE CAPT RETURNED TO THE COCKPIT; HE WAS INFORMED OF THE SIT. THE INABILITY TO CANCEL THE CABIN CALL BUZZER SIGNIFICANTLY CONTRIBUTED TO OUR MISUNDERSTANDING OUR CLB CLRNC. IF THERE HAD BEEN ANY UNCERTAINTY AS TO OUR ALT CLRNC; WE WOULD HAVE ASKED ATC FOR CLARIFICATION. WE ASKED FOR FL370; EXPECTED FL370; HEARD FL370; AND READ BACK FL370. IN HINDSIGHT; WE SHOULD HAVE HAD ATC CONFIRM FL370. WE SHOULD ALSO HAVE THE ABILITY TO CANCEL THE CABIN CALL BUZZER. IT IS VERY LOUD; LASTS TOO LONG AND CAN BE A MAJOR DISTRACTION ESPECIALLY DURING CRITICAL PHASES OF FLT.