Humming noise and monitor interference

I have a digivox Digital Satellite Receiver not sure what model. When i contest it to my flat screen which is also my computer monitor there is some sort of interference - a visible refresh from top to bottom is about the only way. This happens when i plug either a Scart cable in or RCA video cable. Obviously when I remove both (oh yeah tried them alone and together)the waves leave my monitor. This happens even when the power to the box is switched off. I have tried changing the refresh rate on my monitor with ATI Catalyst with no luck. When I do turn it on to watch TV with the computer switched off and the monitor cable unplugged there is a humming noise in the back ground that I have been unable to get rid of after try all the allowed sound options on my TV Sharp 32'' if that's any help
Any ideas on what may be causing this and is there possibly any way to fix these problems