This beeping sound is caused by unplugged cameras. You can deactivate the unused ports by following these few steps. 1) Click on Configure --> Camera/ Audio Install --> Camera/ Audio Install Disable unused ports in cameras and audio by clicking Activate button. Then, hit OK. Uncheck the camera input that does not have a camera plugged in 2) Or, click on Configure --> Video Signal Diagnostic --> check on Disable Video Lost Beep