Popping noise on video (iPhone camera app)

I've searched here and elsewhere online, and can't find the same problem. I have a 2 year old iphone X. Very recently I've found a loud noise when I play videos I have just recorded with the Apple camera app. It's sort of a popping noise (louder than clicking, which several others have experienced.) I'm running IOS14.2, all apps updated. Problem happens using front or rear camera, and also with wifi turned off. A number of people seemed to have had noise problems because of wifi sensor near the mic.

I don't have the same problem using another video app, or with other apps that record audio. Going through old videos, this seemed to start mid-November, but I think I remember occasions before that (but have deleted those videos.)

I have a 10 second sample here: https://www.dropbox.com/s/rwxn0rrl79wjhjd/iPhone%20sound%20test.MOV?dl=0

Have restarted, rebooted, no luck. Not sure if I can delete and re-install the camera app.

Thanks for any suggestions.