Drum drone

Ya hear that? They be hiding something again. Send out a patrol.

Some sounds travel really well through the caves of the Underdark. The sound of drums is one of them.

Because of the reverb and echoes the sound very quickly looses all of its rythm and becomes a distinct droning sound, referred to as drum drone.

Because of the volume and its ability to drown out all other sounds it is quite often used by the denizens of the caves as a way to mask the movement of people, or to act as a distraction.

In order to make sure that when the sound is created it doesn't go in the wrong direction, such as into a settlement, drummers usually have sound reflective planking with them that they can put up behind them.

The droning sounds are not very pleasant, which is why drums are generally not used in settlements, with some cultural exceptions, such as drow using drums in Chamber drumming.