iPhone 5-While using headphones I can hear a noise when the keyboard opens or closes. Sounds like a popping noise-similar to turning on an amp. It is faint, but there. Happens also 5 seconds after you stop typing but don't close keyboard and then again as the first letter is pressed(not keyboard clicking sound). It happens when listening to music and you slide the volume bar to 0 and then just up a little bit. Also happens when while an app is opening. Looks to be anytime something is preparing to make sound. Anyone else notice this?