more about Hydroacoustics for those who want to know
http://uboat.net/articles/id/52
Also: most engines of that era were steam turbines, or steam turbines to electric ... they make zero noise when the ship stands still. Only the turbines used for electrical power generation .. aka auxiliaries are making noise at that moment. Those can be targeted for noise dampening mounting and such, so the sound profile would have been ridiculously small.
Later destroyers were testbeds for Diesel engines. And Torpedo Boats would use gasoline engines, which is a whole different set of crazy. Wood hull for low radar profile + 3 extremely hot running gasoline engines, talk about riding the bomb.