Friends at the Brickboard:

I have a '91 240 Sedan with 170,000 miles on it. It's running just fine, but in cold weather it will frequently whistle when I'm accelerating. I've thought it's likely a vacuum leak, but there's no obvious source. It doesn't happen all that often, and I'm used to it, but I'm motivated to write the BB because the condition has recently changed. It's still chilly here in Kansas City (in the 40's) but it used to only whistle at considerably colder temps. And it's also become more of a chord of tones rather than a single tone whistle. I'll welcome any feedback on what might be making the noise and whether or not it's important that I get it fixed or just live with the quirky sound.

Thanks in advance for sharing your expertise.