This is a new point entity for Quoth 2.2, allowing an ambient sound to be triggered mid-map. Once the sound has begun it will continue for the remainder of the map.
To use a sound with this entity, you must first precache it in a special way: set one of the worldspawn keys noise1 – noise4 to the desired sound file. Then also set the noise key on this entity to the same sound file. (For compatibility with the existing map ne_marb, the noise1 worldspawn key defaults to “necros/drivshft.wav” when not set).