LCD monitors are much more susceptible to interference on the cabling, through mains plugs etc. Slowly moving horizontal stripes are usually due to grounding issues (exactly the same as with buzzing audio equipment). You can try eliminating / reducing them by
- connecting the devices to the same mains socket / extension lead
- connecting the (metal) cases with a somewhat substantial, additional grounding wire
- turning the mains plugs upside down (if possible): unplug everything but the two devices having the problem (no external CD drive, amp, ...) and try all four variations of plug orientation - there should be one combination with minimal interference
