When the engine is idling, the city lights (the position in between the headlights on and off) have a very faint flicker. They don't turn completely off, but go between 100% and probably 80% brightness. The flicker seems to be related to the slight engine idle speed fluctuation (20-30 RPM). The interior lights may also be flickering, but it's hard to tell. When I turn the engine off, they're 100% and have no flicker. I have not noticed the same phenomenon when the HIDs are on, engine running.
Any ideas? Ignition switch? Battery terminal connections are tight.
I did the requisite search, but not that much came back. As always, if I missed something obvious, let me know.