iPhone 11 “radar/sonar” sound

Hi all,

Lately my iPhone has started to randomly make a very low sonar radar pulsing sound. Like it’s searching or getting searched. It is not any of my alarms or apps that are creating the weird sound.

It is always at night it does it, first time I heard it was when I went to bed and everything was quit.

It doesn’t care if I set it to airplane mode or change the volume, I have to turn off the phone and turn it on again before it stops.

Thought it maybe was Find my iPhone but it wasn’t.

any ideas?

best regards

Kristian