For the first time tonight, I heard a strange beep during a phone call. It was a brief number 3 or 4 higher-toned beeps and was not audible to the person on the other end of the call. My Galaxy S3 had WiFi turned on, Bluetooth and GPS were turned off, and there was nobody on call waiting. Lastly, my battery was at 30% and was not low enough to trigger an alert.Any ideas on what this beeping might be? Could this be an instance of monitoring? How could I know if my calls were being monitored?