What was found
REACHING FL450 VERY LOUD ABNORMAL AIR RUSHING SOUND FROM MAIN CABIN DOOR AREA. MORE PRONOUNCED FROM FWD PORTION OF DOOR. NO ABNORMAL PRESSURIZATION OR DOOR INDICATIONS. CABIN ALT 4500'. CABIN DIFF 10.31. SOUND WENT AWAY AS WE DESCENDED BELOW FL410. INSPECTED THE MED DOOR SEAL & INSPECTED VENT DOOR SEAL, NO DEFECTS NOTED. PRESSURIZED THE ACFT. OPS & LEAK CHKD GOOD ON THE MED. COULD NOT DUPLICATE SOUND AT THE MED. COULD NOT DUPLICATE FAULT, INSPECTION OF THE MED WERE GOOD, AND NO HISTORY. WORK PERFORMED IAW AMM 52-11-00, AMM 21-31-00, AND AMM 52-11-69.