What was found
LOUD WHINE COMING FROM CAPTAINS SIDE WINDOW. ISOLATED TO TOP MIDDLE OF WINDOW. STARTED ABOVE 4.6PSI CABIN DIFFERENTIAL. WAS VERY LOUD AT 5.4 PSI AT CRUISE. DIVERTED AND MADE A UNEVENTFUL LANDING. INSPECTED CAPTAIN'S SIDE WINDOW. ALL FASTENERS PRESENT IN WINDOW. TORQUED WINDOW IAW AMM TASK 56-10-06-400-801. STEPS 1-3, STEP 4B (7) (A)-(C) AND STEP 5C. PRESSURIZED ACFT TO 5.5 PSI. NO LEAKS NOTED IAW AMM 21-00-00-863-801. NO DEFECTS NOTED. RETURNED TO SERVICE.