The Listening Monks (or the (Holy) Listeners) are thought to be the oldest religious order on the Disc, except that they're not very religious; they're just trying to make out what the Creator said (whoever he was) to make the universe. Clearly, as nothing the Creator made could disappear completely, the echoes must still be out there. In this quest, they are led by Abbot Lobsang, the 89th bearer of that title. But since he reincarnates, he may have been Abbot for much longer.
To this end, they train their hearing to fantastic sensitivity and live in Enlightenment country in the narrow end of a valley that forms a huge horn, where they listen to the universe. Their temple occupies the same spot in the valley as the armchair of a rabid hi-fi fanatic in his custom-built listening room. Part of their initiation into the monastery is to listen for a coin dropped "at the distance of a thousand yards" and then detect which side it landed on. The Compleat Discworld Atlas tells us they are devoted to The Rite Of Good Vibration.
People have braved numerous perils to trek to the Hub to seek the word of wisdom (which is never to be found at home; always it lives a long way away). They have braved flood, ice, snow, mountains and bandits and suffered deprivations to seek the monks and their wisdom. Until finally, they stagger to the door of the monastery, only to realise that the word of wisdom is Turn the bloody noise down, we're trying to Listen!
The most skilled monks have, when questioned, identified the first sound as: "One, two, ONE, two, three, four..." This is supported by evidence in Soul Music, where Susan, Glod, Buddy and Cliff are stuck in limbo with the formerly Guitar-dwelling Spirit of the Music, and the Creation is replayed for them. Although the Spirit of the Music takes it one stage further back, to the Sound-Check, where footsteps approach invisibly, a voice taps the mike, and then says "ONE, TWO, ONE, TWO" and then recedes again... and then there is the Power Chord that starts Everything off...
This quest would appear to mirror the modern physics quest for background radiation left from the Big Bang.