What was found
MAIN CABIN DOOR STARTED EMMITING A LOUD, HIGH-PITCH, WHINING SOUND ON DESCENT STARTING ABOUT 12,000' MSL, AND BECAME NOTICABLY WORSE AT 6000', AND CONTINUED. UPON INSPECTION, WE FOUND 2 AREAS WHICH MIGHT BE CAUSING THE WHINE NOISE, BOTH INVOLVING THE FRAME'S CENTER RETAINER SEAL: A 4" LONG AREA OF THE SEAL HAS BECOME DETATCHED FROM ITS TRACK, AT THE FORWARD LOWEST LOCKING BOLT RECEIVER PLATE. ALSO, ON THE DOOR FRAME'S AFT SIDE, THE SAME RETAINER SEAL IS RIDING UP ONTO THE ACOUSTIC SEAL IN A 3" AREA, AND POSSIBLY NOT SEALING EFFECTIVELY. APPLIED SEALANT TO LOOSE SECONDARY DOOR SEAL. PERFORMED SATISFACTORY CABIN PRESSURIZATION CONTROL OPS CHECK (ENGINE RUN). WORK PERFORMED IAW AMM 21-30-00, 20-40-30.