During sea trials of a new boat, they have it do passes specifically for sonar to listen to it. Partly so they can learn its sound signature, but also to see if they can hear annomalies during construction. They've found toolboxes left inside a double hull by the builders.

They do have visuals with the waterfall displays and what not. Last I looked into sonar operations was in the early 90s, so not sure what the kids are using now.

They can do all of this without making a sound to allow someone else to know they are there.

The Navy trains to do a series of maneuvers that helps you understand the range to the ships you do hear, and positions the sub most safely to come to periscope depth. And then while you're coming to periscope depth you're looking out to see if there are any indications you've screwed up. But yeah, there's nothing visual available when you're under the water.

My understanding is that US subs don’t travel in packs, so anything they detect is generally the enemy, and especially so if it’s submerged, unless they are escorting a carrier.