  Hot white dwarfs with carbon-dominated atmospheres (hot DQs) are a cryptic
class of white dwarfs. In addition to their deficiency of hydrogen and helium,
most of these stars are highly magnetic, and a large fraction vary in
luminosity. This variability has been ascribed to nonradial pulsations, but
increasing data call this explanation into question. We present studies of
short-term variability in seven hot DQ white dwarfs. Three (SDSS J1426+5752,
SDSS J2200-0741, and SDSS J2348-0942) were known to be variable. Their
photometric modulations are coherent over at least two years, and we find no
evidence for variability at frequencies that are not harmonics. We present the
first time-series photometry for three additional hot DQs (SDSS J0236-0734,
SDSS J1402+3818, and SDSS J1615+4543); none are observed to vary, but the
signal-to-noise is low. Finally, we present high speed photometry for SDSS
J0005-1002, known to exhibit a 2.1 d photometric variation; we do not observe
any short-term variability. Monoperiodicity is rare among pulsating white
dwarfs, so we contemplate whether the photometric variability is due to
rotation rather than pulsations; similar hypotheses have been raised by other
researchers. If the variability is due to rotation, then hot DQ white dwarfs as
a class contain many rapid rotators. Given the lack of companions to these
stars, the origin of any fast rotation is unclear -- both massive progenitor
stars and double degenerate merger remnants are possibilities. We end with
suggestions on future work that would best clarify the nature of these rare,
intriguing objects.
