  We study a stochastic variability of SS433 in the $10^{-4} - 5\times 10^{-2}$
Hz frequency range based on RXTE data, and on simultaneous observations with
RXTE and optical telescopes. We find that the cross-correlation functions and
power spectra depend drastically on the precession phase of the supercritical
accretion disc. When the wind funnel of the disc is maximally open to the
observer, a flat part emerges in the power spectrum; a break is observed at the
frequency $1.7\times10^{-3}$ Hz, with a power-law index $\beta \approx 1.67$ at
higher frequencies. The soft emission forming mostly in the jets, lags behind
the hard and optical emission. When the observer does not see the funnel and
jets (the `edge-on' disc), the power spectrum is described by a single
power-law with $\beta \approx 1.34$ and no correlations between X-ray ranges
are detected. We investigated two mechanisms to explain the observed
variability at the open disc phase, 1) reflection of radiation at the funnel
wall (X-rays and optical) and 2) the gas cooling in the jets (X-rays only). The
X-ray variability is determined by the contribution of both mechanisms, however
the contribution of the jets is much higher. We found that the funnel size is
$(2-2.5)\times10^{12}$ cm, and the opening angle is $\vartheta_f\sim 50^\circ$.
X-ray jets may consist of three fractions with different densities:
$8\times10^{13}$, $3\times10^{13}$ and $5\times10^{11}$ cm$^{-3}$, with most of
the jet's mass falling within the latter fraction. We suppose that revealed
flat part in the power spectrum may be related to an abrupt change in the disc
structure and viscous time-scale at the spherization radius, because the
accretion disc becomes thick at this radius, $h/r \sim 1$. The extent of the
flat spectrum depends on the variation of viscosity at the spherization radius.
