We previously had a 2000 528 BMW and a 2000 Land Rover Discovery, both of which were of course manufactured by BMW. We experienced the same whining sensation at certain speed intervals and my recently acquired 99 E300 does the same thing coming out of 1st gear and at about 80mph. According to 3 different service departments since 2000, all of them said it was the transfer case (gear box). This seems to be a characteristic of German cars. At least as with our experience.

Scott