I'm going to add my two bits to this thread, it is a worthy thread, worthy of a bump.

My 2002 3.0 has this noise, and it is unbelievable that it is there.

Get this.

I complained about it last February when I had a check engine light. Of course I got the Gas Cap fault, and the mechanic said the whistle went away with the gas cap getting screwed in properly. Of course that is BS.

I think half the "Technicians" don't know X5s that well, is this possible?

Thanks to this forum I will check the boot as well. It won't be the first underbuilt piece in this engine that has caused problems.