The interference I had were 100% generated from the M4, since when i tried to power on the monitor from an external psu, the picture was perfect.
Now I just connected an LC noise filter in series between the M4 output and the monitor input.
They should include noise filters with every M4 they sell!
I have a similar problem, and would like to try the LC filter route. Can you please provide more info on this filter? Where did you get it from? Cost? Brand?