Cracking, popping noise and poping nails from the wall
I've been living for almost 5 years in my 2-story single home, which is almost 21 years old, From last year, I've noticed loud cracking noises coming from various locations along my interior and exterior walls and ceilings. The noise only occurs once, although different locations can pop at around the same time.
These noises come intermittently. Sometimes I won't hear anything for hours, and then within the span of a minute, I'll hear several cracking noises along various locations. The noises seem to be coming mostly from the top floor. Recently I also notices that nail pops and small cracks forming at the roof. The noise seemed to started with the hot weather in the summer.
Can anyone tell me what is this? And is there anything I can do to fix it?