shorthair

My 97 C230 has started to make a high pitched squeal noise from the center lower right side of the dash while the blower is on. The noise is very similar to microphone feedback. (It is not a whistling noise.) It is not the radio as it makes the noise when the radio is off. Blower speed does not affect the volume or pitch, but the noise goes completely away when ventilation is set to off. If I set the controls to blow air out the windshield only it does not make the noise. Any other setting (ie: dash and/or feet) will cause the noise. The noise will momentarily stop when the flaps change positions.

Any ideas what I should look at?

Public Enemy

vacuum leak, look behind dash and make sure there is no leak. i had the same problem

shorthair

Thanks for the tip.

I took it apart today and found the leak.