Music that gets “stuck” in the head is commonly conceptualized as an intrusive “thought”; however, we argue that this experience is better characterized as automatic mental singing without an accompanying sense of agency. In two experiments, a dual-task paradigm was employed, in which participants undertook a phonological task once while hearing music, and then again in silence following its presentation. We predicted that the music would be maintained in working memory, interfering with the task. Experiment 1 ( N = 30) used songs predicted to be more or less catchy; half of the sample heard truncated versions. Performance was indeed poorer following catchier songs, particularly if the songs were unfinished. Moreover, the effect was stronger for songs rated higher in terms of the desire to sing along. Experiment 2 ( N = 50) replicated the effect using songs with which the participants felt compelled to sing along. Additionally, results from a lexical decision task indicated that many participants’ keystrokes synchronized with the tempo of the song just heard. Together, these findings suggest that an earworm results from an unconscious desire to sing along to a familiar song.