An hour ago I was walking around my apartment when I heard some music playing very soft. It turned out to be my phone. It was the kind of calm music that you'd hear in the background of a nature program on TV, totally unlike the hardcore stuff I have stored on my phone. The moment I pressed the screen button the music vanished.
I thought it may be a new type of notification I've never heard before, (especially because recently I lowered the notification volume relative to the others), but I found nothing in the notification bar.
I looked at the running programs but found nothing I don't know.
Fearing that it may be a virus or hijack, I installed AVG Mobility antivirus, and it reported that my phone is clean!
Any idea what this may have been?