It's possible one of your windows is off track. You've probably read the discussion of the windows. Yours may be funcitoning properly, but still be off track. You'll know when you examine the trailing edge of the window, as it will have twisted the rubber track. This will cause whistling.

One possible cause anyway. I just had my VX serviced today for the window problem. They replaced the rubber track. My wife drives it more than I do, so I'll find out when I get home, if the problem is solved.