What was found
ON FLIGHT 3844 THE CREW REPORTED THAT AFTER TAKEOFF HEARD A LOUD HISSING NOISE EMANATED FROM THE MAIN CABIN DOOR. THE FLIGHT ATTENDANT REPORTED BEING ABLE TO SEE DAYLIGHT AROUND THE PERIMETER OF THE DOOR SEAL. ALL COCKPIT INDICATIONS WERE NORMAL AND THE DOOR SHOWED TO BE LOCKED ON EICAS DOORS PAGE, NO CAUTIONS, WARNINGS OR AURAL ALERTS. THE CREW DECLARED AN EMERGENCY AND ELECTED TO RETURN TO ORD. THE AIRCRAFT LANDED WITHOUT INCIDENT. THE AIRCRAFT WAS REMOVED FROM SERVICE. INSTALLED MAIN CABIN DOOR SEAL IAW CRJ AMM 52-11-07. THE OPERATIONAL CHECK WAS GOOD PN/ OFF 601R31877-3 P/N OFF 601R318731-1 P/N ON 601R31872-3 P/N ON 601R518721-1. THE AIRCRAFT WAS RETURNED TO SERVICE.