Is there any heavy Appliance like an AC,cooler,refregirator,iron box etc.,?any of theese items cause interferance.
The speaker amplifier (of my zebronics 5.1,it has seperate amp) causes interferance on my LG Flatron (its 2 feet away).

As i said degauss the monitor and see if it solves the prob.Sometimes stray magnetic field developes inside the monitor.