  We analyse light curves covering four years of 39 fast-rotating
($P_\mathrm{rot}< 1d$) late-type active stars from the Kepler database. Using
time-frequency analysis (Short-Term Fourier-Transform), we find hints for
activity cycles of 300-900 days at 9 targets from the changing typical latitude
of the starspots, which, with the differential rotation of the stellar surface
change the observed rotation period over the activity cycle. We also give a
lowest estimation for the shear parameter of the differential rotation, which
is ~0.001 for the cycling targets. These results populate the less studied,
short period end of the rotation-cycle length relation.
