I have a 2004 Explorer with manual heating and air conditioning controls. If I turn the temperature selector dial toward hot or cold when the airflow selector dial is set to any position other than OFF I get a constant clunking noise coming from behind the climate control panel. The noise get louder as I turn the fan speed control from position 1 to 4. I get hot to cold air and any selected temp in between if I set the temperaure selector dial before selecting an airflow setting. What's the fix for this?

CaptainBob