As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
FLT#1537, JFK- STI. (AIRCRAFT PERFORMED AN AIR TURN BACK TO JFK) 'UPON REACHING FL370 INFLIGHT CREW REPORTED EXTREMELY LOUD, HIGH PITCHED NOISE IN THE AFT GALLEY. NOISE DID NOT GO AWAY AS AIRCRAFT DESCENDED UNTIL REACHING ABOUT 5000; FOUND AFT GALLEY WATER DRAIN VALVE STICKING OPEN. R/R DRAIN VALVE IAW AMM 28-11-41 AND PERFORMED CABIN PRESSURIZATION IAW AMM 05-53-00. LEAK CHECK PASS, NOISE NO LONGER PRESENT AND A/C OK FOR RETURN TO SVC.'