have you changed the bulbs to isolate the problem before ruling out what it's not? honestly, that description could be any of the xenon components. more likely to be bulbs and ignitor, but it's possible on the ballast.
what i would do is to swap the xenon components systematically isolate the problem. swap out the bulbs (as it's the easiest to do), if problem changes sides, it's the bulbs. then take out the headlight a swap the ballast (next easiest), if the problem switches sides, it's the ballast. if not, it's the ignitor.
there's a link in my sig for taking out and replacing the components in my sig.