"The Sound of Silence" is a 1965 song by Simon & Garfunkel. Several characters (usually G.O.B.) hear this song as their introspect about their life choices.
G.O.B. hears the song at the harbormaster's lodge when thinking about moving forward with his relationship with Ann. He hears it again at his mother's penthouse in Balboa Towers while thinking about his wedding to Ann. ("Colony Collapse")
G.O.B. hears it while trapped inside the storage locker. Tony Wonder hears the song while explaining to Sally his plans on destroying his life with G.O.B.. G.O.B. thinks he hears it when Ann tells him she has a five year-old son with a magician, but it turns out to be a passing mariachi band. ("A New Attitude")