Yeah the illumination wire - will trace it back as far as I can, and snip it there - at the moment we just snipped it near the head unit end.
seems more noticable when doing above 30mph or so, and doesnt seem to matter what's switched on (heaters, stereo, wipers, lights etc...), and is not affected by braking or cornering.... doesnt seem to be rythmic to the engine as such but it's definately got a beat to it...