As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIR TURN BACK PRESSURIZATION LEAK AFTER APPROXIMATELY 60 MINUTES ENROUTE-INCREDIBLY LOUD SQUEAL MADE COMM DIFFICULT/ATC+ BETWEEN FLT CREW. NOISE STOPPED BELOW 17000 FEET. ACCOMPLISHED T/S AND INSPECTION IAW AMM 56-11-00-210-016 REV 146. FOUND CRACK APP 3 INCH AT LOWER AFT CORNER OF THE WINDOW #2.