i believe your noise is normal.. a lot of cars exhibit it.. not just bmws.. just need to wait for oil to cycle up in there... you can try using a thinner cold weight oil.. like a 0w40 instead of a 5w40.... i think.. don't quote me on that..
however.. if the noise is like mine and some other guys'... vanos rattle at anything around and above 2k.. blech.... most prominent at 2k RPM
click here to hear the ugly vanos rattle
i've already had my vanos unit replaced once, the time chain and tensioner as well.. noise never went away, but was quieted down significantly.. now it's loud as heck again..
If you don't like my driving, get off the sidewalk.