We purchased a 20 year old, 2 story, walkout basement home 6 months ago in Michigan. We have been experiencing loud popping noise in the south facing exterior wall at random times since we moved in. It sounds like the ice on a pond cracking to me. It only happens on this wall of the house. There is only one small window on the entire exterior of this side of the house.

These are some of my theories but all of them seem unlikely and I can't find anything to prove them true. It is driving my wife nuts!!

vinyl siding on outside expanding/contracting with sun or heat changes (but it happens on cloudy days when the temps haven't changed in hours)
house settling (but doesn't seem realist in a 20 yr old house and not evidence in drywall)
changes in interior temps (turned A/C and Furnace way down/up and experienced no sounds)
something in the wall expanding/contracting like ducts or pipes (there are no ducks or pipes in this exterior wall)
Animals in wall ( the noises sometime travel from one side of the wall and travel all the way to the other approx. 25 ft away within a second like ice cracking on a pond)
someone put some type of sound board/insulation in the wall to stop noise from a busy street nearby and this was not designed to be using on an exterior wall and it expands/contracts with changes in humidity or something else. (this seems crazy but it is the only want I haven't tested)


Any thoughts or suggestions on what to do would be very much appreciated. Also, who would you call to investigate this... builder, engineer, HVAC, etc? Thank you!!

I'd go with expansion/contraction of framing or siding.
Which side is the walkout basement facing?
Concrete goes through subtle changes for the first 40 years.
It could even be flooring next tp the outer wall. Mine decided to contract this winter, ugh. Beautiful solid oak installed in 1970, never separated before, but this last summer I had water in the basement, so it may have swelled.

My south facing northern home has almost all the windows, to get the sun. Maybe if you decide to install or enlarge some you will see what you have under the vinyl.