As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
UPON RETRACTION OF LANDING GEAR AFTER TAKEOFF, EXPERIENCED AIRFRAME VIBRATION. AS PRECAUTIONARY MEASURE FLIGHT CREW ELECTED TO RETURN TO IAD. ON ARRIVAL AT GATE FOUND RT NOSE GEAR DOOR OPEN. INSPECTED NOSE WHEEL AREA AND FOUND NO DAMAGE. CLOSED AND SECURED DOOR OPERATION IAW MM 32-22-1.