Us British people losing their accents when they sing?

I never noticed it up until now, but it seems whenever I hum to myself, I seem to lose my accent and I have quite a heavy British accent. My friend, however, joined the secondary school chorus and I seemed to notice that she sang a bit differently. And after school, we both were singing to old Queen hits, such as Bohemian Rhapsody, she still sang in a peculiar tone. I'm still not sure why, I seem to lose my accent when I sing or hum to myself and she seems to not. Any ideas on why this might be?