This is just a variant of 'a flea in his ear', which has been around for about half a millennium. Click http://www.wordwithyou.com/columns/3_1_00.gif
for more information. The basic reference is to a dog scratching annoyedly at an actual flea in its ear.
kind of apropos, I believe that the german phrase for a piece of music or catchphrase that you can't get out of your head is "an earworm" sorry, don't know the german though