  Using the Boltzmann equation with a Langevin-like term describing the
stochastic force in a baryon-photon plasma, we investigate the influence of the
incoherent electron-photon scattering on the subhorizon evolution of the cosmic
microwave radiation. The stochastic fluctuation caused by each collision on
average is found to be small. Nevertheless, it leads to a significant Brownian
drifting of the phase in the acoustic oscillation, and the coherent
oscillations cannot be maintained during their dynamical evolution. As a
consequence, the proposed Doppler peaks probably do not exist.
