What was found
AS AIRCRAFT TRANSITIONED FROM RUNWAY TO TAXIWAY AFTER LANDING, RAMP PERSONNEL & TOWER PERSONNEL SAW WHITE SMOKE FROM UNDER PLANE FOR 20 SEC. CREW REPORTED BRIEF LIGHT SMOKE AND UNKNOWN ODOR IN CABIN THAT DISSIPATED QUICKLY, WHICH WAS VERIFIED BY THE F/O. THE AIRCRAFT CONTINUED TO GATE WITHOUT FURTHER INCIDENT. MAINTENANCE VISUALLY INSPECTED THE APU COMPARTMENT & AIR INLET, BRAKES, AVIONICS COMPARTMENT, CARGO COMPARTMENTS, AIR CONDITIONING PACKS (INLETS & OUTLETS) AND WHEEL WELLS WITH NO DEFECTS NOTED. MAINTENANCE PERFORMED IDLE RUN OF ENGINES PER AMM 71-00-00-710-006, WITH NO DEFECTS NOTED. ACFT RETURNED TO SERVICE. AIRCRAFT HAS OPERATED SEVERAL FLIGHTS SINCE THIS OBSERVATION WITH NO FURTHER INCIDENT.