  Fluctuations in the acoustoelectric current, induced by a surface acoustic
wave propagating along a ballistic quantum channel, are considered. We focus on
the large wave-amplitude case, in which it has been experimentally found that
the current is quantized, and analyze the noise spectrum. A phenomenological
description of the process, in terms of a random pulse sequence, is proposed.
The important ingredients of this description are the probabilities, p_n, for a
surface acoustic wave well to capture n electrons. It is found that from the
noise characteristics one can obtain these probabilities, and also estimate the
typical length scales of the regions in which the electrons are trapped.
