I opened an app, and as soon as I started using it there was a loud sound like a 'bzzzt' alarm - which is not one of the phone's ringtones. I shut the volume off (except the one with the bell) and continued using the app but it still went off every 5 secs, even after I closed and uninstalled the app. I also heard clicking sounds like the one you hear when typing when I wasn't clicking anything. Restarted it and everything is back to normal.