What was found
F/A REPORTS A HISS OR WHISTLE FROM R 2 & L 2 DOOR, THE NOISE STOPPED ON CLIMBOUT AT 19,500 AND BEGAN AGAIN ON DECENT AT 24,5000. ALL ACFT SYSTEMS OPERATED NORMALLY, NO PRESSURIZATION PROBLEMS. ACFT GROUNDED. CLEANED & INPSPECTED L 2 & R 2 DOOR SEAL & SILL. NO DEFECTS NOTED. PRESSURIZED ACFT TO 4.0 PSIG DIFFERENTIAL. NO NOISES HEARD COMING FROM THE L 2 OR R 2 DOOR. HISSING NOISE HEARD COMING FROM THE OUTFLOW VALVE. REPLACED AFT OUTFLOW VALVE IAW AMM 21-31-03-000-801 & AMM 21-31-03-400-801. PRESSURIZED ACFT TO 4.0 PSIG DIFFERENTIAL. NO ABNORMAL NOISES HEARD FROM OUTFLOW VALVE. NO COMMUNICATION OR PRESSURIZATION ISSUES NOTED AT THIS TIME.