Apparently it means there is a dungeon around but I can never find any?
If it does mean dungeons how far away will it trigger?
Ambience (sometimes called cave
noises) is a set of sounds that
occasionally plays when the player is
in close proximity to an unlit cave.
Despite their name, they are not
sounds that one would expect to hear
inside of a cave, such as falling
pebbles, but rather supernatural
noises frequently likened to ghostly
train whistles, rice rockets, and
Ambient sounds require that a space at
least 3×3×3, entirely at light level
zero, be positioned ten to twenty
blocks away from the player in any
direction. The space does not need to
be sealed off – a sound can even play
from a space that the player can
actually see – nor does the player
need to be underground to hear it. The
sounds can also come from
player-created spaces, even if that
space is a box above the clouds.
Contrary to popular insistence,
ambience is not an indicator of nearby
ore, dungeons, or mobs. Following them
can still lead the player to such
things indirectly, since they emanate
from unexplored caves.