I guess blondnboinsd is right, I just got this out of the X5 2005 Owner's Manual:

"Automatic headlamp control* When you set the switch to this position, the system activates and switches on and off the low beams in response to changes in ambient light conditions, for instance, in tunnels, at dawn and dusk, and in rain and snow."

I will have the dealer check it out next time I go in to for service.

Thanks for your help guys.