What was found
DURING CLIMB FROM RJBB, A VERY LOUD NOISE OCCURRED AT THE CAPTAINS WINDOW. NOISE WAS SO LOUD THAT AN INFLT RETURN WAS NECESSARY. UPON DESCENT, NOISE CEASED AT 4.4 DIFFERENTIAL PRESSURE. RETURN WAS NECESSARY DUE TO SAFETY OF FLIGHT DUE TO DIFFICULTY IN COMMUNICATION. INSPECTED SLIDING WINDOW SEAL ON CAPT SIDE AND FOUND SEAL DEFORMED AT FWD LWR CORNER. REMOVED AND REPLACED SEAL MPN ABA7805-1 IAW MM 56-12-01-8. LEAK AND NOISE CHECK OK WITH DP 6.0 OF CABIN PRESSURE APPLIED IAW MM 21-00-00-2.