Hearing sounds in your dreams can be looked at from a spiritual point of view.
Nice sounds are usually positive symbols.
Some may say that in your dream state you have traveled to other higher and more spiritual plains.
Psychologically speaking, you may have heard a song during the day and in your dream state you are simply replaying it.
However, since dreams always have meaning, the song that you are dreaming about may have messages in it that will assist you in solving a problem or will help you to feel better.