asus p5b-vm video wobble

I have recently bought an ASUS P5B-VM with integrated video.

The problem is that the screen 'wobbles' - it is not a nice steady picture. This happens even on the boot and bios screens, so is not a driver issue.

I have tried the same monitor and cables on another PC with no problem. Is there anything except a faulty motherboard that could be causing the problem?

I don't really want to dismantle the whole box to RMA it,in fact I think I'd rather splash out on a cheapish graphics card to avoid the hassle and downtime.

Has anyone any thoughts?

Rgrds

Peter