  We discuss methods to compute significance levels for the existence of
quasi-periodic oscillations (QPOs) in Active Galactic Nuclei (AGN) which take
the red-noise character of the X-ray lightcurves of these objects into account.
Applying epoch folding and periodogram analysis to the XMM-Newton observation
of the Seyfert galaxy Mrk 766, a possible QPO at a timescale of 4200s has been
reported. Our computation of the significance of this QPO, however, shows that
the 4200s peak is not significant at the 95% level. We conclude that the 4200s
feature is an artifact of the red-noise process and not the result of a
physical process within the Active Galactic Nuclei.
