  A dense series of long and high time resolution light curves of the old nova
V603 Aql, covering 22 nights (19 of which are consecutive), are analyzed in
order to identify and characterize variations on the time scale of hours and
days. The well known 3.5 hour modulation, observed many times in the past and
considered to be due to a long lasting, albeit not entirely stable superhump,
is recovered at a period of 0.1453 days and an amplitude of 0.062 mag. Most
interesting, however, is the detection of highly significant brightness
variations with an amplitude of 0.050 mag and a period of 5.85 days which is to
a very high precision equal to twice the beat period between the orbital and
the superhump period. The latter is generally interpreted as the precession
period of an eccentric accretion disk. The origin of these long term variations
remains unknown.
