Somebody relesed a DC sound mod that had the click before the boom of the charge. But I can't find it unfortunately.
It sounded like more of a crack than a click.
IIRC, I read somewhere long ago that the double sound is caused by; the charge detonating....click/crack.....which instantly vapourises the water in the centre of the explosion creating a vacuum, water rushes back in to fill the void.....the roar or boom after. I might be wrong on that though, but underwater sounds are quite different to those we hear through air and things can sometimes sound pretty unusual.