For a while I would get a few bars of a particular song looping in my head after listening to music (more than just the "song in my head" phenomenon that happens to all of us in normal circumstances). It could be Mozart, Bach, or some pop song - especially if I'd listened to it a few times. I would just keep repeating the bars to myself, half-consciously, off and on for a day or two.

This has gotten better as I've improved, but still happens a bit.