  We have found experimentally that the noise of ballistic electron transport
in a superconductor/semiconductor/superconductor junction is enhanced relative
to the value given by the general relation, S_V=2eIR^2coth(eV/2kT), for two
voltage regions in which this expression reduces to its thermal and shot noise
limits. The noise enhancement is explained by the presence of large charge
quanta, with effective charge q*=(1+2Delta/eV)e, that generate a noise spectrum
S_V=2q*IR^2, as predicted in Phys. Rev. Lett. 76, 3814 (1996). These charge
quanta result from multiple Andreev reflections at each junction interface,
which are also responsible for the subharmonic gap structure observed in the
voltage dependence of the junction's conductance.
