Has anyone else experienced what sounds like a whistle caused by rushing air? It doesn't sound metallic. The whistle varies with engine speed, and seems to go away at higher RPM.

I had a similar whistle on my '02 BMW 325ci and it turned out to be a worn intake boot that had cracked and was sucking in air past the air filter, which created a whistle.

I'm wondering if one of the intake tubes has a leak. It has whistled from day 1 and continues to whistle after 6000km.
Thanks.
~Jon