I have iPhone 6 on iOS 10.3. Recently, while watching a video (not stored on my phone, but on YouTube on Firefox browser) with volume set to zero, I put the bottom speaker on the iPhone to my ear (because in the silence of the room, I heard something), and I heard static, despite volume being zero! I closed the tab, which caused the static noise to stop, then opened the Music app and played a song on zero volume, and when I put the bottom speaker next to my ear, the static noise had come back!
Is this normal? Why is there static noise when media is playing at zero volume instead of no noise?
My Bluetooth is turned off, and the Alerts switch (whatever it's called) is turned off (I.e. You can see the orange line next to the volume buttons).