Hugs Boson posted:

HisMajestyBOB posted:

Is 1 suggesting that it's a faulty bit of sonar equipment, rather than a real sound coming from the hull? I slept through that part of Officer School.

It is not! To quote some random book about US Nuclear Submarines:

"Each noise producer must be separated from the hull by noise isolation devices commonly called sound mounts. Attention to detail is the key here. Not only must the small equipment be sound mounted, reducing noises such as flow noise in piping, transformer hum, and so on, but also the largest items such as the main propulsion turbines and turbine generators. [...] To complicate matters still further any single hard, non-isolated connection between a noise source and the hull could defeat the entire program. Such a connection is called a sound short."

So 1 is suggesting that maybe something inside the boat is causing the noise, either accidentally (could happen easily I guess), or by sabotage (as easy as wedging a bolt between the hull and a pipe), or by planting a noise maker.