In the spell Shout, I can make an extremely loud scream
You emit an ear-splitting yell that deafens and damages creatures in its path.
I don't think there's any rules at all for especially loud and magical effects, but what would be considered a fair distance before the perception DC is above 0 in normal conditions? I'm asking as factors like several doors and hallways in a dungeon can limit the distance of a shout, along with forests, and sometimes there's a sleeping dragon or powerful monster nearby that could wake up from this otherwise powerful spell.
On a slightly related note, would it be allowed to yell a specific phrase or word, rather than just a random yell, even though the range is 30 ft. I'm sure that the listed range is simply the deafening effect, not the actual range of hearing the shout (Your ally can stand behind you, and not hear a thing, as it's a cone shaped burst), so not all listeners will be deafened.