I listen to music on my commute every day while also using a handful of various apps. I notice occasionally I can hear this faint melody like a tone coming from my phone playing under the music. It's not app specific and I can't find the tone in my ringtone settings. I use 8.1 developer preview on my Lumia 920. Anyone else notice this? I think the strangest part is that it plays under my music and it's not just the song.