As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING FLIGHT, CREW REPORTED STRONG VIBRATION AND VERY LOUD RUMBLING SOUND FROM BELOW. REPORTED TO BE LOUDEST AROUND ROWS 5-8. NOISE INCREASED WITH ALTITUDE AND SPEED. FLIGHT DIVERTED TO DCA AND LANDED WITHOUT INCIDENT. MAINTENANCE FOUND PANEL 195BR TO BE LOOSE AT THE FORWARD CORNER. ETD2020-170-036096 WAS GRANTED FOR 750FC DEFERRAL OF HINGE SHIMING AND RE-ADJUSTMENT. MAINTENANCE APPLIED SPEED TAPE TO THE PANEL AND PLACED ON DMI FOR 750FC, WITH NO FURTHER DEFECTS NOTED.