We have a fourplex with a flat roof in Calgary, Alberta. The building was built in 1977, but the roof was redone a couple years back before I moved in (gravel-top).
Last winter I was startled awake quite a few times by a loud bang that sounded like someone was swinging a hammer on the roof. It would happen in the middle of the night usually, and happen between ever 10-40 minutes it seemed. It didn't seem to happen during the day. Through the spring/summer I don't think it happened once, but now that the temperature is getting cold again we've noticed it over the last few nights. It started early tonight at around 9PM (which is earlier than normal.. usually it's about 1-2AM).
I'm thinking it's fairly obvious that it's related to expansion/contraction of something in the roof, but my question is what can be done to fix it? It's to the point where I'm sleeping in the basement to avoid being startled... would getting a roofing contractor to come and look at it be worth the time?
One last interesting thing is that it didn't seem to happen when there was a good amount of snow covering the roof (insulation/more constant temp??).
Thanks so much to anyone who can offer guidance.. I'm going nuts here..