The sound is noted in the first word in the Guru Granth Sahib – ੴ, Ik Oangkar. The syllable "Oang" is the sound that was created whilst the universe was created.
In the Guru Granth Sahib's opening word, ੴ, Ik Oangkar, the sound represents what was emitted during the creation of the universe. The syllable "Oang" is believed to have been vocalized at that time.