have a 2008 dodge ram when i turn the heat off it thumps 3 times them does like a growl by the glove box,if i turn the heat/defrost knob it stops sometimes but then starts again with the blower motor switch off,if i play around with the knobs it goes away,but now it has started doing it when the blower motor is on i still have heat to the defrost vents and floor heat is this the acduater going bad i have read a few posts that the plastic gears strip??

possibly.... they are more known for making a "click,click,click" ratcheting noise.