We present the serendipitous discovery of eclipse-like events around the massive white dwarf SDSS J152934.98+292801.9 ( hereafter J1529+2928 ) .
We selected J1529+2928 for time-series photometry based on its spectroscopic temperature and surface gravity , which place it near the ZZ Ceti instability strip .
Instead of pulsations , we detect photometric dips from this white dwarf every 38 minutes .
Follow-up optical spectroscopy observations with Gemini reveal no significant radial velocity variations , ruling out stellar and brown dwarf companions .
A disintegrating planet around this white dwarf can not explain the observed light curves in different filters .
Given the short period , the source of the photometric dips must be a dark spot that comes into view every 38 min due to the rotation of the white dwarf .
Our optical spectroscopy does not show any evidence of Zeeman splitting of the Balmer lines , limiting the magnetic field strength to B < 70 kG .
Since up to 15 % of white dwarfs display kG magnetic fields , such eclipse-like events should be common around white dwarfs .
We discuss the potential implications of this discovery on transient surveys targeting white dwarfs , like the K2 mission and the Large Synoptic Survey Telescope .