What was found
CREW REPORTED, LOUD FLAPPING SOUND HEARD AT 15,000 FT MSL 280 KTS AT TOP OF CAPT'S WINDSHIELD. REQUESTED PRIORITY LANDING, DECLARED EMERGENCY AND LANDED. AFTER SLOWING ASAP, FLAPPING SOUND WAS TOP OUTSIDE SEAL ON NEW WINDOW INSTALLED ON 2/20 IN SDF, DEFERRED AERO DYNAMIC SEAL. INSTALLED MYLAR TAPE.