We just moved into a new home. Whenever the heat comes on, sometime within the first 2-5 minutes you will hear a loud noise. Like a bang or very loud knock. You can definitely tell that it comes from the vent. Also, the noise may come from a different vent area each time?? Thanks, C

Most times this is due to the return air ductwork expanding and contracting or moving in and out due to the "Pull" of the airflow when the furnace blower is running. This is the large ductwork running up the side of the furnace. Next time you turn the heat on, stand by the furnace and see if this is the problem. You should have no problem hearing it. A brace run across the duct and secured will stop the problem.

Will this cause the sound to be louder in one vent one time and then another vent the next?

Yes, it can, depending on where you are located when it happens...