I suppose to detect a noise is one thing, to know what it is is another. The ocean must be full of underwater volcano eruptions, tectonic activity, oil rigs ban

I suppose to detect a noise is one thing, to know what it is is another. The ocean must be full of underwater volcano eruptions, tectonic activity, oil rigs banging and drilling, etc. One of the rescue boats was a commercial cable-laying vessel, presumably laying cables and making noise.