Nothing about position, I used 'background' as a metaphor for something not being attended to.

I understand that; the question was how you made that distinction. Taking your language literally, you said you "pushed" those things to the background. One observation of NLP is that quite often (though not always), people describe their mental processing quite literally, even though their language is "metaphorical".

NLP also observes that if you take those descriptions literally and then perform the same "metaphorical" steps in your own mind, you can often more-or-less reproduce the subjective experience of the other person.

So when I read what you said, I realized that there are times when I more or less literally "push things to the background", but that I had never done so with a song in my head. So it seems worth trying, whether it actually has anything to do with how you push things to the background.