courtesy of wikipedia,
Earworm, a loan translation of the German Ohrwurm, is a portion of a song or other music that repeats compulsively within one's mind, put colloquially as "music being stuck in one's head."
Use of the English translation was popularized by James Kellaris, a marketing researcher at the University of Cincinnati, and Daniel Levitin and the boss CTK. Kellaris' studies demonstrated that different people have varying susceptibilities to earworms, but that almost everybody has been afflicted with one at some time or another.