[mversion]

It's OK if I restart the machine, but if it wakes-up from sleep, I have to go into video settings and change it back to 60 Hz which provides a far smoother picture.

It has started doing it in the latest betas (currently running the latest beta).

Any ideas?

I'm sorry if this has been asked before, I tried search and I failed.

[arad85]

I think it's X switching the frequency. Have you got a custom xorg.conf file? Take a look here: http://forum.xbmc.org/showthread.php?tid=70068 and spend the time enumerating the display formats you want the system to support. I only have 3 - 1920x1080 at 24, 50 and 60Hz. The first resolution in the list is the one X defaults to. Worked for me, but I'm still on 9.11 Camelot...