What was found
AIRCRAFT WAS GROUNDED: AIRCRAFT WAS NOT PRESSURIZING AND AT 9300 FEET A LOUD HOWLING NOISE BECAME AUDIBLE IN THE FLIGHT DECK. DECESION MADE TO RETURN TO JFK AIRCRAFT LANDED WITHOUT INCIDENT. FOUND CONDENSATION TUBE DISLODGED AND INTERFERING WITH L2 WINDOW CLOSURE AND AN IMPROPER SEAL CAUSING THE LOUD HOWLING. AFTER REPOSITIONING AND SECURING DRAIN TUBE AIRCRAFT PRESSURIZED AND THERE WAS NO LONGER A LOUD HOWLING ALL OPS NORMAL.ACCOMPLISHED PRESSURIZATION SYSTEM MANUAL MODE TEST PER MM 23-33-00710-801 AND PRESSURIZATION SYSTEM GROUND TEST PER MM 21-31-00-700-802. ALL TEST PASSED AIRCRAFT PRESSURIZED NORMALLY.