What was found
EMER DECLARED AT DESTINATION LOCATION. LANDING UNEVENTFUL & ACFT WAS NOT OVERWEIGHT. ON TAKEOFF AT ROTATION, A BANG WAS HEARD IN CTR OF ACFT & VIBRATION FELT IN COCKPIT. GEAR DOWN FLYBY OF TOWER SHOWED NO DAMAGE TO TIRES & FLIGHT CONTINUED. INSPECTION FOUND AFT CARGO NETTING UNSECURED WITH BAGS SCATTERED. SUSPECT BAGGAGE STACK COLLAPSED ON TAKEOFF. PROPERLY SECURED CARGO NETTING IN AFT CARGO BIN.