  Current fluctuations are studied in a mesoscopic conductor using
non-equilibrium Keldysh technique. We derive a general expression for the
fluctuations in the presence of a time dependent voltage, valid for arbitrary
relation between voltage and temperature. Two limits are then treated: a pulse
of voltage and a DC voltage. A pulse of voltage causes phase sensitive current
fluctuations for which we derive microscopically an expression periodic in
$\int V(t)dt$ with the period $h/e$. Applied to current fluctuations in
Josephson circuits caused by phase slips, it gives an anomalous contribution to
the noise with a logarithmic singularity near the critical current. In the DC
case, we get quantum to classical shot noise reduction factor 1/3, in agreement
with recent results of Beenakker and B\"uttiker.
