Noise between floors (층간소음) has been a social issue in Korea for many years. Most of the time, the noise comes from children playing and the parents genuinely feel bad about it and try to keep the kids quiet. Sometimes though, you are blessed with neighbors who don't give a rip, or can't even grasp the concept of consideration for their neighbor. Happens everywhere, I guess, but as the article says, in Korean cities the majority live in these high rise apartments, so it's a more frequent issue.