Banging pipes at 4am

[motocrossmann]

When the temperature outside gets below 35F at night, I get a single bang/rattle in the wee hours of the morning in my copper pipes. Under no circumstance can I get the same thing to happen by opening/closing faucets or flushing toilets. My leading thought right now is that maybe the cooler nighttime temperature is causing my copper pipes (under the house) to shrink ever so slightly and a sticky hold down clamp is causing the "bong" as the pipe slips in it. Am I crazy, or are there other explanations?

 

[Caduceus]

You're not crazy. During cold spells your house can make all sorts of noises related to contraction of metals and wood inside the home. Copper pipes will do the same, but it probably isn't at the strap that holds the pipe. I have found that most of the "bang" noises come from the area of pipe where there is a 90 bend or tee (perpendicular junctions) and at copper-to-brass connections.
Some plumbers may say this type of bang is more common on the hot side piping or the cold piping closer to the hot water tank. ( Could be related to the Mpemba Effect). By insulating the water pipes in the basement you may provide more consistent temperatures and less exposure to drafts on the pipe if the bang really concerns you.
Link for Mpemba Effect: http://en.wikipedia.org/wiki/Mpemba_effect

 

[motocrossmann]

My concern was more around damage that might be occurring to the solder joints. It sounds like I probably should not worry about it.

 

[Caduceus]

Well, just keep your eyes and ears open. If this is the first year that you have experienced this problem, try to think back to if and when there may have been changes in the house (new water heater, addition to home, changes in landscaping around yard, etc.)
It's always good to familiarize yourself with where the main water shut off as well as other emergency utility shut offs. I don't know what region you live in, but it's due to get colder next week and I've never had frozen/burst water lines, but I'm still taking precautions as if it will happen. Never hurts to be prepared.