Sound really does travel that far.
To answer your question, since it's now open, a normal human can hear Silbo (a whistled language) from up to 5 miles away. Sound really can travel that far.
However, lower frequency sounds take less energy to travel longer distances: an alligator mating call, for example, can be heard for miles -- and that's at frequencies humans can hear.
If Superman's ears are super sensitive, they are also likely able to hear frequencies that human can't -- and thus he would recognize these sounds by their longest-traveled frequencies that he could hear; this is consistent with the behavior of animals with greater-than-human hearing, like dogs responding to a dog whistle from large distances.