I bought an apartment and I'm in the process of renovating it.
One weird thing I noticed in one of the rooms is that when I hit the wall with my fist lightly, the entire wall and maybe even the room vibrates and resonates for a good second or so afterwards. This doesn't happen anywhere else.
On the other side of the wall, there is a closet. There is another room on the other side of the closet, hitting the wall there doesn't cause vibration. This is a brick and concrete apartment building in Europe, Floor 7 of 9. The building is 50 years old. The wall is made of bricks.
Anyone have any ideas or explanation on why that might be happening?