FLC OF AN MLG RETURNED AND LANDED AFTER HEARING A LOUD AIR NOISE AROUND A REAR EMER EXIT DOOR AND DIFFICULTY IN ACFT PRESSURIZATION.

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WE PICKED UP AN MD-80 IN RNO FOR THE FLT FROM RNO-PDX. IT WAS A COLD AIRPLANE WHEN WE ARRIVED AT THE GATE. THE FO PERFORMED A WALK-AROUND WHILE I DID THE ORIGINATING COCKPIT CHKS. SINCE THE AIRPLANE HAD SAT OVERNIGHT; IT WAS NECESSARY TO SVC THE LAVATORIES; POTABLE WATER; AND DE-ICE THE ACFT. AFTER THIS WAS COMPLETED; A SECOND EXTERIOR INSPECTION WAS DONE PRIOR TO DEP. AFTER TKOF; PRIOR TO REACHING 10000 FT; THE CABIN CALLED AND SAID THAT THEY HAD A MASSIVE PRESSURE LEAK AT THE R REAR EMER EXIT. I NOTED THAT THE CABIN WAS CLBING AT A FASTER RATE THAN NORMAL AND WAS NOT HOLDING NORMAL PRESSURIZATION. I PROCEEDED BACK TO THE CABIN TO VISUALLY INSPECT THE SIT. IT WAS QUITE EVIDENT THAT IT WOULD BE NECESSARY TO RETURN TO RNO. THE NOISE LEVEL WAS SO GREAT THAT IT WAS NEARLY IMPOSSIBLE TO TALK WITHIN 6 ROWS OF THE LEAK. I RETURNED TO THE COCKPIT AND WE INFORMED APCH THAT WE WOULD NEED TO RETURN TO RNO. I ALSO MADE A PA INFORMING THE PAX OF OUR PLAN TO RETURN. THE APCH AND LNDG WERE UNEVENTFUL. AFTER ARRIVING AT THE GATE; MAINT FOUND THAT THE EMER EXIT WAS NOT PROPERLY INSTALLED. AT NO TIME WHILE WE WERE ON THE ACFT WAS THE EMER EXIT REMOVED. IT WAS INSPECTED FROM THE EXTERIOR TWICE BEFORE DEP AND APPEARED FLUSH AND PROPERLY INSTALLED. THE FLT ATTENDANTS ALSO CHKED IT FROM THE INTERIOR AND EVERYTHING WAS NORMAL IN APPEARANCE.