  We analysed an X-ray light curve of the dwarf nova RU Peg taken by XMM-Newton
with a duration of 46300 s. The power density spectrum has a complicated shape
with two red noise and two white noise components, indicating the presence of
two turbulent regions. We developed a statistical "toy model" to study light
curves with variability produced by an unstable turbulent accretion flow from
the inner disc. Our results are consistent with a disc truncation radius
maximally 0.8 x 10^9 cm. We found that any fluctuation of the viscous mass
accretion at the inner disc are visible as UV and X-ray variations with the
same break frequency in the power density spectrum. This process is generating
low frequency variability. A second break suggests the presence of a faster
X-ray variability component which must be generated by another process likely
localised between the inner disc and the white dwarf.
