We investigate the effect of isolated scattering centers on the electronic transport in metallic carbon nanotubes. It is found that the impurity potential significantly alters the overlap of electronic wave functions and results in a rapid oscillation in the conductance and the shot noise. Furthermore, the conductance and the shot noise near the neutral Fermi energy depend periodically on the relative position of the scatterers and on the phase factor ϕ which is generated by the scattering. If two defects are in the same sublattice and Δd≫ac, the conductance near the neutral Fermi energy is dropped to G0=2e2∕h approximately and the shot noise decreases to zero when ϕ=1, but the conductance decreases to zero if ϕ=ω or ω2; whereas, the situation is reversed for the configuration in which two defects are in the different sublattices. For the case of closely paired defects, it is predicated that a small “energy gap” would be developed in “metallic” nanotubes. A comparison of our numerical results and the analytical calculations of the effective-mass approximation is presented.