As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
FLT#2288, JFK-AMS. (AIRCRAFT PERFORMED AN AIR TURN BACK TO JFK) 'FLIGHT ATTENDANT DETECTED A STRONG AIRFRAME VIBRATION ON CLIMB OUT OFF DUTY PILOT CONFIRMED UNUSUAL NATURE OF VIBRATION NO DOORS OR PANELS INDICATED ABNORMAL PRESSURIZATION NORMAL THROUGH LEVEL OFF CAPT ELECTED TO RETURN TO JFK TO HAVE AIRFRAME CHECKED OUT.' (SUPPLEMENTAL INFORMATION TO FOLLOW)