In our new house, there is a loud bang when the AC shuts off after each cycle. It is loud and like someone is hitting the duct work close to the AC/Furnace. How can we stop this?

(((In our new house)))

If the house is new call the builder or the company that put in the equiptment. The problem is DUCT POP or any one of a dozen names for the noise you hear. It is caused by the stop of airflow from the blower motor when it stops running. Usually the metal duct will have to be reattached properly or cross broke to prevent the oil can type pop. You can check the blower motor to make sure all is well in that department but the duct in my opinion is usually where the problem is .

Thanks. Upon further inspection, one section of the duct is doing exactly as you describe.
It is being sucked in when the A/C is on and pops out when it goes off.
THanks for your help.