I suspect this is more of a Debian kernel issue rather than an OMV issue but it's happening on my Dell M4800 Precision laptop that I have been using as my OMV / compute workhorse.
In the last week, I've rebooted the system twice. Both times at a certain point late in the boot cycle the screen starts flickering like mad. (Mainly horizontal lines, all different colors.)
I ran the hardware BIOS full system check, nothing shows as having problems.
Googling turned up a few people on Ubuntu forums having similar issues, which they traced to "something" in the kernel. (Nobody had a definitive fix.)
I booted into the SystemRescue CD and ran startx ... that started up fine, no issues, so whatever is causing this is coming later in the boot cycle.
I'm not a kernel / drivers / hardware guy, never saw this happen until the last 7 days. Given that the BIOS h/w diagnostics say everything is fine, I don't think the screen is dying.
(I had made no changes to the underlying system setup since I installed OMV, it's just been running some VirtualBox images and Samba shares.)
I'm at a wall of what to do.