A320 CREW EXPERIENCES JOLT VIBRATION ACCOMPANIED BY ECAM MESSAGE WARNING FOR L OVERWING EXIT. FLC ELECTS TO RETURN TO SEA.

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CLBING THROUGH FL344 FOR FL370 IN SMOOTH AIR; THE ACFT EXPERIENCED A LOUD MOMENTARY THUMP JOLT FOLLOWED BY A MOMENTARY VIBRATION. IT WAS A HARD SUDDEN THUMP JOLT THAT DISPLACED THE ACFT AND HAD AN AUDIBLE THUMP NOISE. SIMULTANEOUSLY WITH THIS HARD JOLT; THE L AFT OVERWING EMER EXIT OPEN ECAM WARNING ILLUMINATED AND REMAINED ON. WE IMMEDIATELY LEVELED OFF AND NOTED THE CABIN PRESSURE WAS NORMAL AND REMAINING NORMAL. THE HARD JOLT WAS SIGNIFICANT ENOUGH TO ASK THE 'A' FLT ATTENDANT TO COME TO THE FLT DECK AND CONFIRM THERE WERE NO INJURIES AND VERIFY THE CABIN WAS SECURE. THE 'A' FLT ATTENDANT VERIFIED NO INJURIES AND ADVISED THE WHITE SLIDE INFLATION LIGHT ADJACENT TO THE L OVERWING EMER EXITS WAS ILLUMINATED. AS A PRECAUTION; WE DSNDED TO THE MEA; DECLARED AN EMER AND RETURNED TO SEA. APPROX 1/2 WAY BACK TO SEA; THE ECAM WARNING EXTINGUISHED. FLT ATTENDANTS ADVISED THAT IS APPROX THE SAME TIME THE WHITE SLIDE INFLATION LIGHT EXTINGUISHED AS WELL. OVERWT LNDG ACCOMPLISHED AT SEA. LNDG WT WAS 143400 LBS. LNDG WAS NORMAL. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATES THAT THE CLB UP TO THE TIME OF THE INCIDENT WAS SMOOTH AND THAT THE JOLT EXPERIENCED WAS MUCH LIKE XING WAKE TURB WITH PERPENDICULAR MOTION. HE STATES THAT THE CREW WONDERED WHETHER THEY HAD IMPACTED SOMETHING OR SOME PART HAD SEPARATED FROM THE ACFT AND DISCUSSED THE POSSIBILITY OF LOSS OF PRESSURIZATION AND DONNING OF OXYGEN MASKS. THE FAA CTLR MADE NO MENTION OF OTHER TFC IN THE VICINITY OF THE INVOLVED ACFT. ON CHKING WITH MAINT AT A LATER DATE; THE RPTR LEARNED THAT NOTHING WAS FOUND TO BE OUT OF THE ORDINARY ON GND INSPECTION. THE ACFT WAS FLOWN THE NEXT DAY; AND THAT FLC EXPERIENCED THE SAME MALFUNCTION OF ECAM WARNING LIGHTS DURING AN ENCOUNTER WITH MODERATE CHOP. AS A RESULT; A SENSOR OR SWITCH AT THE L AFT EMER OVERWING EXIT WAS REPLACED AND THE RPTR KNOWS OF NO FURTHER ACTION OR DIFFICULTIES WITH THE ACFT. HE STATES ALSO THAT HE IS UNAWARE OF THIS TYPE OF OCCURRENCE WITH THIS ACFT OR ANY OTHER OF THE A320 FLEET.