As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIRCRAFT WAS GROUNDED: AN EMERGENCY WAS DECLARED DUE TO: LOUD VIBRATING NOISE SIMILAR TO VIBRATING FAN HEARD FROM NOSE CLIMBING THROUGH 20000 FEET. SOUND CHANGED WITH CHANGES IN AIRSPEED. AIRCRAFT RETURN AND LANDED SAFELY AT MIA WITHOUT FURTHER INCIDENT. FOUND EXTERNAL POWER DOOR NOT COMPLETELY LATCHED. NO DAMAGED NOTED, DOOR VERIFIED PROPERLY CLOSED. PER AMM 52-49-02.