Yeah, I've seen the cabin filter TSB as well. Usually you get no air out of the vents as the first clue.

GM - I think you're on the right track with that car. If the whistle is tied to very strong manifold vacuum, I too think you're chasing a vacuum leak. Fortunately, I've never been under the dash of a 210, so I can't offer any advice. Make your friend buy you a mity-vac and go from there.

- JimY