Hello and Welcome to Justanswer, My name is XXXXX XXXXX X am here to try and assist your with your question.The noise you are describing is caused by a bad blend door acuator in most cases and this will cause the heater to blow cold air, I can send you instructions but need to know if you have manual air (knobs) or electronic (buttons).
I have enclosed the replacement instructions , to replace the acuator , the instrument panel has to come out .Download HERE and HERE
My skills with cars are limited to changing oil and replacing wipers. Sounds complicated. Should I have it done by a mechanic? If so, what could I expect to pay for this service?
The labor runs about 6 hours and you can figure about $85 for the part.
So +/- $ 600.
Yes that a good ball park figure.