As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
FLT 6749 - IAD-GSO - DURING CRUISE, AIRCRAFT MADE AN UNSCHEDULED LANDING DUE TO HOWLING NOISE AT 250K. AIRCRAFT RETURNED TO GATE WITH NO FURTHER PROBLEMS. MAINTENANCE INSPECTED AND FOUND EXTERNAL POWER DOOR OPEN AND CLOSED DOOR. NO DAMAGE TO DOOR OR AIRFRAME. OPS CHECK OK. AIRCRAFT WAS RELEASED AND APPROVED FOR RETURN TO SERVICE. (M)