There's a small opening at the top for sound to escape, just not her.And the sound waves would reflect back and propagate away from Superman’s ears given the position of the concrete slab. But more importantly, IF Lois could somehow produce the required force against the resistance of the water to produce sound, the thick concrete would dampen, not amplify it. And that’s what’s between her and Superman, not the chamber of water. Also, it was established in MoS that Superman had to train himself to focus his mind and block out all the extraneous audio inputs he was receiving with his “super hearing”, so he wouldn’t have been listening for a presumably safe Lois in that situation anyway.
Look, at the end of the day this is still a comic book movie so it’s pointless to keep debating how the science would work within it. Let’s just agree to disagree.
That doesn't mean he hasn't trained himself to use it to his advantage.
Fair enough