Weird Bubble Sound Happens Randomly
every once in a whiel, randomly, my iphone will make a weird bubble sound. it's not the sound that it makes when you send a text message, it's some other sound.
but it happens randomly. i can't figure out what's triggering it. and nothing happens when it makes this sound. the screen doesn't turn back on, i get no notification, no text, no email, no messages from anything, nothing from any of my apps
i have no idea what this random sound is. does anyone have any idea what this is or what it means?
iPhone 4, iOS 5.0.1