AN AIRBUS A-320 FLT CREW EXPERIENCED ACRID SMELL WITH A HUMMING; GRINDING SOUND BEHIND COCKPIT FLOOR AT TWO DIFFERENT DSCNT LEVELS FOLLOWED BY A 'VENT EXTRACT FAULT' ECAM. EMER DECLARED.

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DURING PREFLIGHT NOTED MULTIPLE FAILURES ATTRIBUTED TO VENT EXTRACT FAULT. CLBOUT WAS UNEVENTFUL. IN CRUISE WHILE TALKING TO CTR WAS GIVEN A DSCNT TO FL360 AND NOTICED FAINT ACRID SMELL. DONNED O2 MASKS AS A PRECAUTION AND WITHIN A MINUTE THE SMELL HAD DISSIPATED. REMOVED MASKS AND NOTICED HUMMING/GRINDING SOUND APPEARING TO EMANATE FROM FLOOR AREA BEHIND COCKPIT. FO SENT TO BACK AND SHE FELT A VIBRATION ON FLOOR AFT OF FWD GALLEY AREA. WE SUSPECTED A FWD LG DOOR ISSUE. UNEVENTFUL DSCNT FROM FL360 TO FL240. WAS GIVEN SUBSEQUENT DSCNT TO FL200. DURING THIS DSCNT GRINDING AND HUMMING NOISE INCREASED AND SMELL RETURNED MORE INTENSELY. RE-DONNED MASKS AND HALFWAY INTO DSCNT ALL NOISE SUDDENLY WENT AWAY FOLLOWED WITHIN A FEW SECONDS BY A VENT EXTRACT FAULT ECAM. ECAM DIRECTED US TO TAKE EXTRACT FAN TO OVERRIDE WHICH WE DID AND WE THEN DECLARED AN EMER DUE TO FUMES IN THE COCKPIT AND ASKED FOR EQUIPMENT TO STAND BY. DURING THIS PERIOD WE BRIEFED EACH OTHER; CREW AND PAX AND THEN NOTIFIED THROUGH ACARS COMPANY AGENCIES (DISPATCH AND MAINT CTL). ACFT WAS ALWAYS IN POSITIVE CONTROL BY A CREW MEMBER DUE TO POSITIVE ACFT CONTROL CHANGES. SINCE FULL CONTROLLABILITY WAS AVAILABLE AND FUMES WERE DISSIPATING ELECTED NOT TO PREP CABIN. LANDED UNEVENTFULLY AND HAD EMER TRUCKS FOLLOW US TO GATE. AT GATE; SHUT ACFT DOWN AND MAINT WAS BRIEFED AS TO ACFT CONDITION. DURING COCKPIT DEBRIEF WE FOUND THAT WE WERE BOTH EXPERIENCING A LOW GRADE HEADACHE AND SOME THROAT AND NOSE IRRITATION.SUPPLEMENTAL INFO FROM ACN 765582: AT FL380 A LOUD NOISE BEGAN; WITH A GRINDING AND VIBRATION FELT. SYSTEMS WERE NORMAL. A FAINT SMELL OF SMOKE DETECTED BY MYSELF; WE DONNED O2 ESTABLISHED CREW COM. NO VISIBLE SMOKE; SMELL DISSIPATED. WE SPOKE WITH FLT ATTENDANTS TO SEE WHAT THEY HEARD AND SMELLED. MASKS WERE REMOVED. NO SMELL ONLY NOISE/ALL SYS NOTED NORMAL. FLT RETURN TO NORM WITH THE NOISE; FO SENT MSG TO MAINT. CAPT CONTINUED TO FLY. FO WENT BACK TO CABIN TO INVESTIGATE NOISE. I CAME INTO COCKPIT; WE BEGAN DSCNT TO FL200; NOISE GOT VERY LOUD; WE ADVISED ATC THAT WE WERE WORKING AN UNKNOWN PROBLEM AND NEEDED TO SLOW TO 250 KTS. SMELL OF SMOKE GOT INSTANTLY WORSE. WE IMMEDIATELY DONNED O2 ESTABLISHED COM; AIRPLANE THEN GOT VERY QUIET; FOLLOWED BY AN ECAM. I DECLARED AN EMER AS PER CAPT REQUEST AND TOLD THEM TO STAND BY; WE PERFORMED THE VENT EXTRACT FAULT ECAM. THE CAPT WAS FLYING; WE TRANSFERRED CONTROLS UPON COMPLETION OF ECAM; I FLEW; CAPT PERFORMED DISPATCH; MAINT; FLT ATTENDANT BRIEFING. I GAVE SOB; FUEL REMAINING; REQUIRED EQUIP; NOTIFIED THEM OF SMOKE IN COCKPIT. FROM FL200 TO GND; THE SMELL DISSIPATED WITH THE EXTRACT FAN IN OVERRIDE AS PER COMPLETED PROCEDURE. WE DEEMED IT SAFE TO REMOVE THE MASKS; THE CAPT TOOK POST CONT OF ACFT AND AN UNEVENTFUL ARR AND LNDG IN ZZZ OCCURRED. WE CONTINUED THE GUIDANCE OF EMER EQUIP UNTIL THE ACFT WAS SAFELY AT THE GATE. UPON COMPLETION OF COCKPIT DEBRIEF; WE BOTH NOTED A LOW GRADE HEADACHE; AND IRRITATED SINUSES AND THROAT.CALLBACK CONVERSATION WITH RPTR ACN 765579 REVEALED THE FOLLOWING INFO: RPTR STATED THE PREVIOUS 30-DAYS OF MAINT HISTORY OF THIS ACFT SHOWED MULTIPLE FAILURES ATTRIBUTED TO VENT EXTRACT FAULTS. YET; ALL OF THE FAULTS WERE CLRED. DURING DSCNT TO 20000 FT THE GRINDING AND HUMMING GOT VERY LOUD; AND THEN; JUST STOPPED; VERY ABRUPTLY. THE ACRID SMELL CAME BACK AND THE ECAM 'VENT EXTRACT FAULT' APPEARED. THE ECAM DIRECTED THEM TO TAKE EXTRACT FAN TO 'OVERRIDE;' WHICH THEY DID. EVEN IN THE 'OVERRIDE' MODE; THE SMELL DID NOT GO AWAY; BUT; AT LEAST THE ACRID ODOR DID NOT INCREASE. RPTR ALSO STATED COMPANY MAINT FOUND THE EXTRACT FAN BEARING HAD FAILED.