As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
PASSING THROUGH 21,000 FT, THE CREW FELT A VIBRATION. SHORTLY AFTERWARDS, THE FLIGHT ATTENDANT REPORTED TO THE CAPTAIN THAT A DOOR WAS OPEN ON THE SIDE OF THE AIRCRAFT. THE CAPTAIN MADE THE DECISION TO RETURN TO TULSA TO DETERMINE THE DAMAGE DONE.