  We have investigated random telegraph noise (RTN) observed in individual
metallic carbon nanotubes (CNTs). Mean lifetimes in high- and low-current
states, shigh and slow, have been studied as a function of bias-voltage and
gate-voltage as well as temperature. By analyzing the statistics and features
of the RTN, we suggest that this noise is due to the random transition of
defects between two metastable states, activated by inelastic scattering with
conduction electrons. Our results indicate an important role of defect motions
in the 1=f noise in CNTs.
