Why do the walls of my north and south bedrooms always have the sound of hammering?

Is it because there are pipes in the wall? There may be noise when there is water falling in the pipeline or the air column vibrates. When it rains on cloudy days and the air humidity is high, the water vapor in the pipeline is easy to condense into water droplets, which may be more obvious. Due to the influence of temperature or humidity changes, the volume of wall materials may also make your voice.

As you said, 15 minutes is really annoying. I suggest you go to the property and ask your neighbors if there is a similar situation. If you can't handle it, I can only suggest you buy the right earplugs ... After all, there is an unexplained banging in my closet in the middle of the night. Wearing earplugs can at least get a good sleep. I hope it will help you.