Subsequent soundproofing of water pipes

The houses are so close together that the neighbor's sink drain pipes run directly through our shared wall.

I imagine that to be terrible. From a distance, I cannot assess whether wallpaper alone is sufficient. :( I am in favor of installing a stud wall, as this significantly reduces the noise level.

As if these water noises are so massive, then only a stud wall will help. I do not consider such a wallpaper to be sufficient. Of course, the room will become smaller again due to such a wall and adequate insulation.

However, here it is a matter of weighing the reduction of this noise level against the loss of space.