I generally have a soundtrack in my head, and what you describe happens to me occasionally, but not as much as it happens to you, I expect.

I always loved the story about the crew who were taking Ranulph Feinnes, the polar explorer, to drop him off at the start of one of his unaided attempts at reaching the pole. They knew that he always had the last song he heard running through his head for most of the expedition, so they made sure that the last thing he heard was a song he hated.