It’s really quite simple to establish if it is feedback or not. If it does it when you are in your car, when you are outside of the house, then there is no possible way that it can be feedback, in the usual sense. Could be something odd going on at camera only level, not involving the app, but again, if it still does it when you sit in your car, outside, with the camera inside the house, it is not feedback.
If it does it when you do that, you can then go back to support and advise them of same.
Next, can you invoke a recording from the app? With an XT2, you can ask it to save a live view. If you can, turn off the volume on your phone, completely, and set it to save your live view. If that live view recording, still has ‘feedback’, again, it isn’t traditional feedback, and second, you will now have a video that you can upload to youtube, and be able to send support the link.
Post it up here too. Hearing it will be interesting, and will help others.
As a matter of interest, when I have feedback, real feedback, when I am near a camera with the app, it always builds incrementally, from 0 to very loud, over a good 5 or 10 seconds. I can reset it to the start of this timeline, repeatedly, by simply putting my thumb over the phone’s speaker.
If ever I am doing some test where I need to be near, that’s all I do to stop it, but this is with correctly working items, which is seemingly not your issue.