Noise-heater control

My wife has a 2004 LeSabre. There is a noise coming from the dash which sounds like plastic rubbing as if there is a poor fit on the dash cover. It is not loud but it is irritating. It begins a few seconds after the ignition is turned on. I discovered that it goes away when the temperature control is over to hot and comes back when the lever is back to cool. Car does not need to be running. Any ideas?