Auto-translated
Ant nest.
By the way, we have decent neighbors, knock on wood. Only sometimes I hear someone having a tantrum, but it's nothing major. No partygoers, no people using power drills, and no babies. At the same time, the soundproofing seems to be good. The worst neighbors are the pigeons; in the spring, they coo above my head, and in the summer, they run loudly across the balcony.