I noticed a slight "whistling" type noise (not very loud but I notice it) coming from the engine when I hit the throttle (doesn't matter if I'm parked or on the road). 

So, I stopped by the dealership and had the shop forman listen to it.  He said he's familiar with it and it's due to the alternator.  And he said there's nothing that can be done.  I asked if BMW corporate is aware and he said yes but they won't do anything about it as there is nothing mechanically wrong with the alternator so they chalk it up to an "engine characteristic".  I have a hard time buying the explanation but he wasn't going to do anything about it.

So, do any of you know about this "enging characteristic"?  Have you experienced a similar issue?  If so, were you able to correct it?  Any advice would be welcome.

Thanks...

Funny you posted this, I also had the same problem and after many many stops at the dealer, They found it! 

I do not know now what they did to fix it but I will call them (Foreign Motors West) Today and get that answer for you!

They replace many past for free untill they found it!

You can call me direct if you wish at 791-413-5218, Might be faster!

Larry!