Undocumented SOS sound

now and then when booting, I get an looping SOS morse sound.
What is that , and how to make it boot properly ?

means corrupted SD card.

copter.ardupilot.com/wiki/common … PX4_Sounds

or missing card

run chkdsk if the card has been corrupted.

Thank you.
For reference, would a format be ok too ? - or would something else than logs be missing ?