What was found
AIRCRAFT RECEIVED FUEL, CREW THEN TAXIED AIRCRAFT TO ACTIVE RUNWAY TO WAIT APPROXIMATELY 15 MINUTES. AT NO POINT DURING THEIR WAIT DID THE REFUEL DOOR ILLUMINATE ON EICAS. AFTER DEPARTING RUNWAY AT 400-500 FEET ABOVE GROUND, THE REFUEL DOOR INDICATION ILLUMINATED ON IECAS. FELT A VIBRATION IN THE AFT RIGHT SIDE OF AIRCRAFT FOR APPROXIMATELY 2 TO 3 SECONDS. UP TO THAT POINT, ALL AIRCRAFT INDICATIONS WERE SMOOTH AND NORMAL. ELECTED TO CONTINUE SHORT LOW LEVEL FLIGHT BACK TO HOME BASE AT A REDUCED AIRSPEED, DID NOT FEEL IT WAS A SAFETY OF FLIGHT. AFTER ARRIVAL, INSPECTED AIRCRAFT TO DISCOVER THE REFUEL DOOR HAD DEPARTED AIRCRAFT. TEMPORARY REPAIRED.