Since updating to iOS 5, my phone will give me a sound. Not long maybe 1 sec long. It has no banner, badge or other notification. What's even weirder, is that I went into sounds, and I can't find the sound in my sounds. It doesn't do it often, but has done it maybe a total of 10 times. Has anyone else had this happen. I'm sure it's a functional sound, so I'm wondering what my phone is trying to tell me. Any help would be appreciated. Thanks Oh, it's an iPhone 4 on Verizon.