VeryGnawty
1) The cable connecting the monitor to the computer could be damaged or wearing out.
2) The monitor could be going bad.
3) Make sure that your equipment is at least six feet away from any 2.4GhZ cordless phones, wireless adapters, or cell phones. These devices can cause interference in the cables connecting your computer to your interface devices (mouse, keybord, monitor, etc.) Always keep your computer equipment away from any similar devices which emit high frequency waves.
4) Make sure that you don't live close to any radio towers, cell towers, or "ham" radio operators using powerfull radio equipment. These devices have been known to cause interference with other electronic systems.