Please note that when the surrounding environment is rather quiet, the camera would automatically raise the sound. Just like the sound in your video; While if the sound is too loud, the camera would lower the sound that comes from the outer environment.

You could take videos in noisy areas to see if that is the case. Or you could say something to the camera when taking pictures. There won't be the sound that occurs in your video.

Another possible reason for noise in recorded videos from action cameras is the use of waterproof housing. The housing can muffle audio recordings or create a vacuum effect that can generate noise.

Please try to record without waterproof case.