Do you have Navi? The Navi disc in my X runs when I unlock the door, before starting the car... presumably loading the maps before you need them. I can hear it from time to time when I'm at a light with the radio muted too.
(or is the navi in the 2013 HD based?) I am not sure :/
Alpinweiß 2005 325Ci
Spacegrau 2007 X5 3.0Si