As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING CLIMBOUT, COCKPIT CREW HEARD AND FELT A LOUD VIBRATION. LEVELED OFF AT 24K FT. KEPT AIRSPEED AT 280. RETURNED TO DEPARTURE UNEVENTFULLY. ACFT GROUNDED. ON RETURN TO GATE, FOUND EXTERNAL POWER DOOR OPEN. PERFORMED A GVI OF DOOR AND SURROUNDING AREA. NO DAMAGE NOTED AND OPS CHECKED GOOD. OK FOR SERVICE, IAW AMM 05-51-67.