  In this work we have investigated short time-scale variability of NGC 4051
and NGC 4388. The quasi-steady QPO's time scale of 3920$\pm$17 sec was detected
for NGC 4051. For the case of NGC 4388 we investigated rapid variability of the
parameters of spectral models. To obtain these results, a new "Moving Fit"
method for processing of the trailed X-ray spectrograms was developed.
