I've always considered a diesel-electric boat running on batteries to be quieter than its nuclear counter-part at the time. Even the 6th or 7th gen reactors all had a bit of sound, didn't they? Batteries was totally quiet if the crew shut up and you had a decent prop that wouldn't cavitate below 10 or 15 knots.
Of course, now they've got these natural convection nuke plants that can operate at a fair percent of full power without the Achilles Heel of
submarine-based reactors: the coolant pumps. In exercises didn't the USN actually look for black holes in the ocean, where the normal ambient noise
of the ocean was replaced by a black hole?
Now that's saying something about how advanced Ohios are, even nowadays.