When the 'Enable Web Alarm Notifications' is enabled on the Palo Alto Networks it will send a beep through the host PC speaker every 10-15 seconds. As long as Palo Alto Networks is connected to the HTTPS the beep will continue.
Details
To stop the beep, disconnect the connection to the WebGUI.
To 'Enable Web Alarm Notifications' open a window to display alarms on user sessions, including when they occur and when they are acknowledged.
To define Alarm Log Settings, Go to Device > Log Settings > Alarms: