  We present results from several years of fast optical photometry of
4U0614+091 (V1055 Orionis), a candidate ultracompact X-ray binary most likely
consisting of a neutron star and a degenerate secondary. We find evidence for
strong accretion-driven variability at all epochs, that manifests itself as red
noise. This flickering produces transient peaks in the observed power spectrum
in the 15-65 min period range. Only in one of our 12 optical datasets can we
see evidence for a period that cannot be reproduced using the red noise model.
This period of 51 minutes coincides with the strongest period detected by
Shahbaz et al. (2008) and can thus be taken as the prime candidate for the
orbital period of the system. Furthermore, we find some tentative evidence for
the X-ray vs. optical flux anticorrelation discovered by Machin et al. (1990)
using our data together with the all-sky X-ray monitoring data from RXTE/ASM.
We propose that the complex time series behaviour of 4U0614+09 is a result of
drastic changes in the accretion disc geometry/structure on time scales from
hours to days. Finally we want to draw attention to the interpretation of
moderately strong peaks in the power spectra of, especially accreting, sources.
Many of such "periods" can probably be attributed to the presence of red noise
(i.e. correlated events) in the data.
