The S'glhuoans are a fictional race created by Chaosium in 1995 for the Call of Cthulhu RPG, whom are based on Ramsey Campbell's The Plain of Sound.
S'glhuoans are a race which exists in a world located in the Gulf of S'glhuo, a universe in which every world and inhabitant is made up of sound. To humans they appear as quasi-reptilian humanoids, though being sentient creatures made of living sound. They can mentally project messages which humans pick up as dreams over incredible distances.
Without the aid of a special device known as a "translator", they cannot travel outside their home universe. The "translator" must be activated on planet they desire to visit, and it's built by those whom receive their dream messages. As they consist of living sound they cannot be harmed by physical attacks, only by magic and specific discordant sounds. The denizens of S'glhuo use bursts of sound waves in combat. Tru'nembra is worshiped by the sound creatures.