I often see something written down that reminds me of a song (e.g. title, words) and it's almost invariably a song I don't want in my head, but now it's triggered. But usually I can 'over-write' it with a different choice of song, if I try hard enough.
But then I almost always have a 'music track' going in the background of my head, with whatever I'm thinking in front of that, as it were. The best was a piece of music, thoroughly unidentified except I thought I might have played it as part of our recorder consort at school. Earlier this year I bought off eBay the G4 descant pieces I played in 1990, and there it was!!! I was utterly delighted to find it, it's one of my "fallback earworms". It's Chaconne from The Fairy Queen by H. Purcell. But it's been intermittently going round my head since 1990 with me having no recollection of what it was

I remember finding it really hard to get to sleep one night because I was thinking so much, so I started breathing slowly and counting slowly to relax myself, but then the counting slowly switched to my 'background' track and my head was then counting slowly in the background and back to spinning over whatever I was thinking about before!!
The term earworm, incidentally, originated in German.