I don't think the drone records sound. Other wise all you would get would be props noise.
Sound can be added later when you edit vid.
At least that's the way I've always been informed....
It would be in the manual for sure so read up some more.
What R U flying ??
My understanding is DJI uses the video's audio track channel for telemetry. You can find early videos on youtube with audio but they are taken with cameras such as the gopro which include audio.