My phone did that a few weeks ago! I wasn't smart enough to look it up and see why it happened. I asked DH, who swore I must have installed some app, but I knew I hadn't.
I was driving when it happened. The sky was dark and gray, so when I heard the noise, I knew it was a weather warning. The surprising part was that I was listening to my iPod on the stereo system--not the radio. I wondered how I was getting a radio warning when the radio wasn't on. I turned the volume all the way down and then realized it was coming from my phone. It was just a flood warning, and since I was 2 miles from my house (that's on the top of a hill), I didn't really worry about it. It would be nice for tornadoes. We can technically hear the sirens from my house, but with 5 boys, sometimes our own noise level is too high to hear them. We just moved to a town that doesn't have reverse 911 service, so I was wondering what I should do to get weather alerts.