As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DEN - FLT 522 - AFTER MAINTENANCE AIRCRAFT TOOKOFF AND HAD LOUD NOISE FROM NOSE GEAR AREA. SUSPECTED NOSE GEAR DOOR NOT UP. AIRCRAFT MADE AIR TURN BACK. FOUND NOSE GEAR DOOR NOT LOCKED UP AND INSPECTED THE AREA AND LOCKED NOSE GEAR DOOR UP. (M)