  The Kepler mission was launched in 2009 and has discovered thousands of
planet candidates. In a recent paper, Esteves et al. (2013) found a periodic
signal in the light curves of KOI-13 and HAT-P-7, with a frequency triple the
orbital frequency of a transiting planet. We found similar harmonics in many
systems with a high occurrence rate. At this time, the origins of the signal
are not entirely certain.
  We look carefully at the possibility of errors being introduced through our
data processing routines but conclude that the signal is real. The harmonics on
multiples of the orbital frequency are a result of non-sinusoidal periodic
signals. We speculate on their origin and generally caution that these
harmonics could lead to wrong estimates of planet albedos, beaming mass
estimates, and ellipsoidal variations.
