On top of what Sam said, the only reason I can think you might see interference on a LCD
would be down to the signal being interfered with on the way rather than the monitor
itself. You mention only one speaker causes the problem, does the speaker in question by
any chance have the monitor cable run behind it/cable tie'd near it? I suppose a analogue
VGA cable might be able to pick up interference.
Are you using a VGA
(D-SUB)cable or a HDMI/DVI? If it's the former try changing it for one of the later.
--------------------ScanProAudio & 3XS Audio Systems