From SRB2 Wiki
Thing type 708, Disco Ambience, is a type of Thing that plays an ambient disco sound effect when the player is in range. The sound it plays is
sfx_ambint; the corresponding lump is
DSAMBINT. In SRB2, it is used in Egg Rock Zone Act 2's disco room.
|Thing types – Miscellaneous invisible||[view]|
|Water Ambiences A - H • Disco Ambience • Volcano Ambience • Teleport Destination • Alternative View Point • Zoom Tube Waypoint • Push Point • Pull Point • PolyObject Anchor • PolyObject Spawn Point • PolyObject Spawn Point (Crush) • Skybox View Point|