When we turn on the heater theres a loud knocking in the dash and rear of the vehicle. Hot air is being blown but it just knocks really loud. Im thinking it might be the AC/ Heater Acutuator Motor
Does the noise change with the blower speeds? If so, it needs a blower motor - I owned one once that was so loud it sounded like I had an exhaust leak - from out side the vehicle with the windows all up !