I have this noise in my car when it is cold out (<30 degrees outside temp). It seems to go away when the car gets warm or I park in my heated garage. It sounds like a soft whistling sound. Generally you only hear it when you turn the radio and climate control off. I checked out the archives and all I really got was the interior temp sensor may have been going bad. I removed that and it still makes the noise. It almost sounds like it is coming from the center of the dash, under the dash pad, to the right of the instrument cluster. I had a vacuum diaphraghm replaced under warranty for a similar kind of noise, but I can't seem to locate that in the service manual which makes troubleshooting kinda difficult. Thanks in advance for any info or ideas.

Find the small (about 1") square grill next to the steering wheel and listen in there. That is where the asperator fan is. A stethescope will amplify it nicely.

Ranger - You call it an asperator, I call it an interior temp sensor. Disconnected it, the sound still exists.

Did you disconnect the sensor or the fan that draws in interior air and passes it over the sensor? I would think they are seperate but I could be wrong.

Now that I think about it, I have a similar faint whistle when cold and the fan comes on high. I suspect mine is from the blower. It's very faint and short lived so I have chosen to ignore it. Not sure if we are talking about the same thing.

Ranger - In my initial post I stated the climate control was in the off position. I disconnected the fan/sensor (it's one unit) and tested it on the bench. It was fine. My main reason for this posting was to find out if it is possibly a vacuum leak.

Unplug the HVAC blower and see if there's a difference. Even with the system off, it still turns at a slow speed to keep ventilation going in the car.