This has happened twice now. The car sits out in the heat for a little while and then when I get in and crank up the air will only blow (loudly) through the windshield vents. This will go on for about 2 minutes while I turn every dial and attempt every setting to try to get it to blow through the main vents. Is this normal? Is it some genius thing that BMW has designed that I will appreciate after I know what it is?