Sound

NetHack has no sound in the sense of audio-output from speakers, but your character in the game will hear many sounds, such as:

You hear water falling on coins.
You hear the splashing of a naiad.

Most sounds have a definite meaning. All of the above tell you that there is a fountain on the level. The next reveal that there is a vault:

You hear the footsteps of a guard on patrol.
You hear someone searching.

Other sounds can indicate one of many events, such as:

You hear a chugging sound.

This means a monster quaffed a potion, but you don't know which one.

You hear crashing rock.

There's a dwarf or some monster somewhere on the level that is creating tunnels through walls.

You hear someone cursing shoplifters.
You hear the chime of a cash register.

There's a shop on this level.

You can use this wiki to look up what a sound means by typing its message into the search box. You should be redirected to an article about the thing that caused the sound.