intermittent high pitched whine from heater

[rbnbird]

My 98 E320 heating/cooling system has started making an intermittent high pitched noise. It is happening only while heating not cooling. Any idea what might be causing this?

[talonlover]

I would say a blower motor but before I would diagnose anything I want you to try something. The next time you hear the noise put your ear up to the interior temp. sensor(On your car I think it's on the headliner built into the dome light assembley) There is a very little blower motor that circulates air over the sensor, sometimes it starts making a high pitched noise, it's so high it's hard to tell the orgin of the sound) If that is the cause you can replace the sensor for around 70.00 parts and labor. Hope that helps.