When walking around the Deep Dark with the difficulty set to "Peaceful", with no regard to staying quiet, you will sometimes hear Warden sounds as a result of setting off the Sculk Shriekers (you can tell these are Warden sounds because of how they're identified in the subtitles). No Warden actually shows up, of course, it's just the sounds that are there when they shouldn't be.
I haven't tested other settings, but I wouldn't be surprised if the same issue can be found with things like the doMobSpawning game rule, and other options that prevent the Warden from spawning. To be clear I'm referring to any sound effect that's credited to the Warden in the subtitles, and not any other Sculk-related noises.
For what it's worth, I think you could argue for keeping this as-is, but I figured monster sounds where there are no monsters is probably unintended.