  We investigate the correlations in the current fluctuations at different
terminals of metallic diffusive conductors. We start from scattering matrix
expressions for the shot noise and use the Fisher-Lee relation in combination
with diagram technique to evaluate the noise correlations. Of particular
interest are exchange (interference) effects analogous to the Hanbury
Brown--Twiss effect in optics. We find that the exchange effect exists in the
ensemble averaged current correlations. Depending on the geometry, it might
have the same magnitude as the mean square current fluctuations of the shot
noise. The approach which we use is first applied to present a novel derivation
of the 1/3-suppression of shot noise in a two-terminal geometry, valid for an
arbitrary relation between the length and wire width. We find that in all
geometries correlations are insensitive to dephasing.
