Pixhawk mysterious voice and automatic landing

Hello guys,

I don’t know if it is appropriate to ask this problem here,
I try to connect my Pixhawk(APM:Copter V3.5.3 ,PX4V3) with my Raspberry Pi 3 and use Dronekit to control it.
However, when it start to takeoff, my pixhawk made some voice, it sounds like four short beeps, after that, it automatically landing. I test my script in SITL. It works normally.

So, I start to check Pixhawk, first I try to find the sound meaning hereofficial, but there are no one matches.

Did I do something wrong? What’s that voice meaning?
I’m confused for a week.
I appreciate your advice, any suggestion is good, thx a lot.

Here is the test video

the appropriate logs should be needed to help you