Help to identify unknown tone from Pixhawk

The following link to the video recorded the tone from my Pixhawk which is of the first generation.

The tone does not match any of the 14 tones listed in the wiki (under AutoPilot hardware options—mRo Pixhawk). Pls listen and pay attention to the 2nd half which is clearer and louder. The 3 cell flight battery was at 11.7 V and the tone in question does not resemble the low battery tone. There is no error message in the “Message” tab of MP. I can arm and disarm the motor. This tone is emitted not only during bench test, also sometimes during flight.

When I change to a battery at 12.4 V, I got “Bad battery” message in the HUD of MP. See attached.

Any help is appreciated.

The Hud reads 0.02v . Maybe bad connection somewhere. I think I have heard that alarm when running motors flat out with no propellers. I now keep the throttle lower on bench test.