Just got awakened by two loud bangs, so I decided to get up (4:30am). Turned on the computer and checked the news and weather. It's minus 28! Aha, the bangs were the I-beams in the building contracting. One Winter, one old dear phoned 911 to report gun-shots being fired upon hearing these noises:). Anyway, have a nice warm day wherever you are...Cheers.
Ours, here in the western U.S. usually don't start barking and banging until about -25 (F). I found that, on older homes, it's often the plywood sheeting on the roofs that are contracting and announcing their move at 2:00AM. Funny, isn't it that when they move back to the original position (as it must) when the weather warms, there's nary a sound?