Our neighbouring galaxy M31 (Andromeda), located 780 kpc away, offers a unique opportunity to study the X-ray population of a galaxy similar to the Milky Way. We have concentrated our monitoring campaign on following the X-ray activity of the stellar-mass black hole candidates, XRNe (X-Ray Novae), in the central region of M31. Observations are made approximately once a month with Chandra, following up any bright outbursts with HST in order to identify the optical counterparts. Having measurements of the X-ray and optical luminosities in outburst allows for the estimation of a system's orbital period. There are now 9 systems with a known or constrained orbital period in M31 and it is finally possible to compare their distribution with that of the Milky Way black hole systems. We show how the latest 3 orbital period estimates were obtained and compare both populations.