Banging noises are related to air in the system permitting a column of water to move at high velocity agains elbows and other fittings. Sometimes raising the water pressure in the system stops the banging by compressing the air, making it easier to move the air away from the banging location.
Since the banging occurs mostly at night, the water temperature of the system is hotter because the outdoor weather is colder and the burner runs longer to heat the water. There may be some banging in the system as the air bubbles become larger in the hotter water. Sometimes the water doesn’t move fast enough through the boiler and the banging results from local bubbles of steam collapsing as they hit the hot, but cooler, water in the boiler. The cure can be moving the water faster and moving the bubbles out of the system.