Interference on external VGA monitor (intermittent ripple) only when booted into MacOS X but OK on Windows Bootcamp, why? and how to fix?
Under OS X, open Terminal.app and enter the following command:

defaults write NSGlobalDomain AppleFontSmoothing -int 2


Then, reboot your Mac.

This will enable subpixel font rendering on non-Apple LCDs. This simple tweak solved a lot of display issues for me back when I was using an external Dell display at work. I hope it helps you, too!