K3 "beep" reason?

[AB3EN]

Several times a day my K3 gives a loud beep with no error message or visual sign of a problem. K3 is in RX mode when it happens, and the KPA500 is online but idle since the rig is in RX mode. Temps are fine both in room and indicated. Anyone have an idea what is causing the "beep"? 12V power supply is fine and as it should be.

Low battery on K3 motherboad?
Thanks
AB3EN