How strange, I have exactly the same thing! Sounds like the old radio countdown's before the news started.
Tried turning everything off, only thing left on the idrive menu is a 'T' which I can't figure out (I know, "look in the manual"). Thought it was traffic reports so turned all those off too, I don't even have the navigation menu in now, or the telematics active... so probably something in the radio.
ETA: Ahaaahaaha. Search is my friend... http://www.e90post.com/forums/showth...highlight=beep
It's in fact an hourly reminder that can be set from the i-drive menu