is also difficult to constrain the significance of possible QPOs due to power spectra effects [@vaub]. EXOSAT data of NGC 5548 were reported to have a significant period [@pap93], but @tag96 later showed that the significance of the candidate QPO was lower than previously reported once the uncertainties in modeling the spectrum were taken into consideration.

This lack of statistically significant evidence for QPOs in AGN has led to questions of whether existing X-ray observations of AGN are sensitive enough to detect QPOs even if they are present [@vau05].

Here we use a different technique to search for significant periodic structures in the time variability data that have been collected for AGNs with XMM-Newton. We use a wavelet transform technique, which can have certain advantages relative to periodograms and Fourier power spectra, the methods that have previously dominated the literature. The wavelet technique, which has become widely used in other branches of science, is particularly useful in identifying signals where the period or its amplitude changes with time. This technique is applied to the XMM-Newton data from bright 10 AGNs, with special care taken to properly treat the noise characteristics and error analysis, and we find a candidate 3.3 ks 