As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
FLIGHT 3445, AT TAKEOFF HEARD A VERY LOUD NOISE IN COCKPIT THAT SOUNDED AS IF THE GEAR DID NOT COME UP OR A DOOR WAS OPEN. LANDING GEAR INDICATIONS WERE ALL GREEN AFTER GEAR RETRACTION. DECLARED AN EMERGENCY, RETURNED, AND LANDED WITHOUT INCIDENT. AIRCRAFT REMOVED FROM SERVICE. REMOVED AND REPLACED THE PROXIMITY SWITCH ON UPLOCK BOX IAW MM 32-63-03. OPS CHECKED GOOD. AIRCRAFT RETURNED TO SERVICE.