Every once in a while when I turn on my a/c or heater I hear a whiny noise under the hood that gets whinier at higher rpms. It almost always stops when I turn the heater off. what is it and how expensive is it to get fixed?

 

Well, when you turn your AC on it activates the compressor under the hood. Typically...it makes a little noise("clicks" on and off), but isnt really supposed to making a whining sound. More info may help in diagnosing your problem.