I have this problem too, my right headlight only. Ive seen a thread about it on audizine, not sure if theres a fix for it. Iv heard that people bring it to the dealer and the dealer either a) says theres no problem because they can't recreate it in the shop or b) charge like 800 bucks to replace the ballast in the headlights and that still doesn't fix the problem.
Ive learned to deal with it.... i modded my headlight switch so that my fogs work without the headlights being on, so when my headlight flickers, i turn the headlights off, wait a second, and turn them back on. that sometimes fixes it.