What was found
(CAN) ON AUGUST 17, 2012, ACFT WAS ON DEPARTURE AND AT FL 20 A LOUD WHISTLING SOUND WAS HEARD FROM THE MAIN CABIN DOOR. THE PILOT FLYING, ELECTED TO RETURN TO DEPARTURE FOR MAINTENANCE TO CHECK THE PROBLEM. THE TUBE FOR THE CABIN DOOR SEAL WAS FOUND NOT SEALING PROPERLY AND POSSIBLY KINKED. THE PROBLEM WAS RECTIFIED BY SEALING THE TUBE AND CONFIRMING PROPER ROUTING. ACFT WAS RELEASED SUBJECT TO TEST FLIGHT. THE TEST FLIGHT WAS UNEVENTFUL WITH NO DEFECTS NOTED.