What was found
PASSING 10K MSL, EXTREMELY LOUD SQUEAL APPEARED IN COCKPIT. PRESSURIZATION NORMAL. CLIMBED TO 14K AND SQUEAL REMAINED ON. NOISE WENT OUT PASSING 10K MSL IN DESCENT. SHUT OFF ALL RADIOS & COULD NOT ISOLATE PROBLEM. PRESSURIZED A/C TO 8.5 PSI NO SQUEAL OR HISS NOTED FROM ANYWHERE, IN REFERENCE TO B-727-200 M/M 05-51-101-2, ALSO COMPLIED WITH AIRFRAME DECAY CHECK IAW B-727-200 M/M 05-51-101-2 NO DEFECTS NOTED. INSPECTED AND CLEANED BOTH COCKPIT SLIDING WINDOWS AND FRAMES, NO DEFECTS NOTED. OPENED WINDOWS AND CHECKED SEALS FOR INTEGRITY, NO FAULTS FOUND. OPENED AVIONICS DOOR UNDER COCKPIT AND CHECKED, NO DEFECTS FOUND. PRESSURIZED A/C AGAIN TO 8 PSI, NO SQUEAL OR ANY ABNORMAL SOUNDS.