As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
PILOT REPORTED THAT AFTER TAKEOFF, A VIBRATION WAS FELT THROUGHOUT THE AIRFRAME. ELECTED TO RETURN TO DEPARTURE. ALL PANELS AND DOORS WERE INSPECTED FOR SAFETY AND SECURITY AS A PROBABLE CAUSE OF VIBRATION, NO DEFECTS NOTED. INSPECTED ENGINES. RT ENGINE SPARKPLUGS WERE FOUND TO BE WORN. ALL TWELVE SPARK PLUGS WERE R & R. ACFT OPS CHECKED GOOD.