What was found
(CAN) DURING CLIMB, A LOUD NOISE HEARD THROUGH 15000 FT. NOISE WAS VERY LOUD, ALMOST LIKE A HORN SOUND. AIR TURN BACK PERFORMED. ON DESCENT, THE NOISE ABRUPTLY STOPPED THROUGH 15000 FT. MAINTENANCE FOUND INSULATION BLANKET UNDER THE ESCAPE HATCH SEAL. CONDITION CORRECTED. ALL WINDSHIELDS RE-TORQUED AS A PRECAUTION. PRESSURIZATION TEST CARRIED OUT, IAW THE AMM WITH NO ABNORMAL NOISE EVIDENT. AIRCRAFT RETURNED TO SERVICE. (TC# 20181015011)