Warning: Contains spoilers!
In the Selenitic Age, while you are going through the maze to get back to Myst Island, and you use the "directional sounds" to figure out which way to go through the maze.
However, these sounds are taught to the player in the Mechanical Age. It's entirely reasonable that one would visit the Selenitic Age, and therefore wouldn't have been able to learn the sounds which indicate direction beforehand.
Therefore, it would be unreasonable if there was not also some indication in the Selenitic Age of which noise points in which direction. However, I cannot seem to find it.
Where is it? :)