I don't have ADHD (at least I don't think I do :P) and I have the same problem and have as far back as I can remember. When I was a kid I would sometimes forget that it was only in my head. It isn't always the same song, but there is a constant background soundtrack in my life and it has been there for years. Sometimes it's just a series of repetitive notes. As I write this, I'm listening to U2's "New Year's Day", involuntarily of course. Often it will be a song I dislike, which is annoying, or even worse two songs at once. The point is that it never stops, sometimes not even when I'm dreaming, and it is there as soon as I wake like switching on a radio.

I have told other people about it and they found it odd, so I thought I'd mention it to the psychiatrist, who then recommended cognitive behavioural therapy. I haven't gone yet. Most of the time it isn't a problem, and sometimes it's even nice; I can listen to Mozart in my head, and it is just as moving to me as if I were listening to a recording, louder than the horrible radio stations my co-workers insist on blasting all day long. But other times it gets incredibly frustrating because I have little to no control over it and it can cause great anxiety for me, even keeping me from sleeping.

I hope you will look into the situation if it is causing you distress or interfering with your daily life. I'm going on my second day of U2 at this point, so I understand where you are coming from, for sure.

I am also very curious - what song is it that you are stuck with?