For about 3-4 months, I've been getting an audible tone that appears to notify me of nothing. I can only describe it as a short (less than half second) guitar chord. What is baffling is that, A) no visual notification accompanies the sound, and B) the sound occurs even when the phone is silent. It is not a timer or alarm that I have set as all of those have been deleted. I have been unable to show it to anyone since I had no idea when to tell someone to listen as I couldn't discern a pattern or schedule...until now. Over the weekend, I figured out that it is happening at :11 past every hour. Again, I have no alarms set and no reminders or anything like that, so I'm completely lost. I appreciate any help.