As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
WHILE CLIMBING THROUGH FL 300 AT A SPEED OF MACH 0.78, EXPERIENCED AIRFRAME VIBRATION. SLOWED SPEED TO APPROXIMATELY 0.74 MACH AND VIBRATION WENT AWAY. AIRCRAFT RETURNED TO MEM AND LANDED WITHOUT INCIDENT. MAINTENANCE TIGHTENED THE FASTENERS ON A BELLY PANEL. FURTHER TROUBLESHOOTING REVEALED NO DISCREPANCIES.