What was found
(AIRCRAFT 6822, L/P 6532920) AFTER T/O VIBRATION AND HI PITCHED HUMMING FROM LEFT SIDE OF A/A. COULD FEEL VIBRATION IN FLT. CONTROLS, RUDDER PEDALS AND AIRFRAME. AFTER LEVEL OFF, WENT AWAY, NOTHING ON DESCENT. CORRECTIVE ACTION: DURING W/A FOUND LT SIDE PACK INLET ACCESS DOOR MISSING. ALSO PANEL DAMAGE. 665422. REMOVED PANEL, ROUTED TO SHOP. REINSTALLED PANEL.