Place it at the start of a mystery sequence, then follow it with a Dun Dun Dun sting when the theory or reveal appears, so the unknown sound sets up the payoff. For a lighter ocean edit, end with a short bell ding after the reveal to mark the moment clearly.
About this sound
This is a ten-second underwater recording called Julia, a mysterious sound from beneath the ocean surface that is difficult to place and easy to replay in your head. It feels eerie and unsettling, giving a quiet moment a tense edge, as if something vast and unseen is moving somewhere far below.