Phone occassionally ceases to ring

[TurboFool]

My phone occasionally simply doesn't bother to ring or vibrate. The screen shows an incoming call, but there's no other feedback to alert me to the incoming call. So far each time I've soft-reset the phone to clear it up, although it's possible something else might have resolved it.

The only two factors I've noticed that correlate, but may not have any connection to the problem, is that I have my Bluetooth connected (although I nearly always do anyway), and the phone has happened to be plugged into either the wall or my car charger at the time.

Anyone else experienced this?