Actually, I know what you're talking about, as it happens often to me. Last spring I was in a 170 mile bike ride for two days and couldn't get a piece of music I had practiced the night before out of my head--I was sort of on cruise control and nothing much else goes through your head out there other than the scenery and the pain, so I couldn't shake the tune. Learned it pretty well by the end of the ride, but I have no idea how to get rid of the tune until I listen to some more music or I get involved in something that makes me concentrate my thinking.