Mostly at night, I have a very, very loud banging sound from the attic. It seems to be wood popping, but it is unbelieveably loud and happens constantly all night long in the winter. The house is only 5 yrs old. We have a second furnace in the attic for the second floor. It is so loud, it is actually frightening and I am concerned it is more than just wood popping from shrinking.

I'd call back the folks who did the work originally. Could be under warranty but likely not. This sounds like faulty installation and expansion when the attic furncae is on. Is the attic well vented and are there intakes in the eaves. The attic must remain as close to the outside temp to function properly. You got too much heat escaping.