As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
LOUD NOISE AND VIBRATION IN FLOOR FROM AFT F/A SEAT ON BACK, STARTED WHEN POWER APPLIED DURING T/O RUN. SLIGHTLY MORE NOTICEABLE ON C/P SIDE DURING FLIGHT NOISE AND VIBRATION WOULD INCREASE AS POWER INCREASE AND DECREASE AS THROTTLE RETARDED. FOUND PNEUMATIC DUCT SEPARATED. REPAIRED SAME.