I run Cycliq cameras, so this is probably N/A, but I have a rattling sound coming from inside one of my two Fly12CE's.

My understanding is that it's a sort of a hardware-based mechanical image stabilizer, that moves around inside the camera 5-10 mm, and tells the camera where to crop the edge of each the frame off, in order to make the video image appear stable. My Fly12CE reportedly shoots in a much higher resolution (4k?) than the 1080p video I get, but the oversized frame is used for image stabilization purposes, FWIW.

I'm wondering if maybe the GoPros use something similar to smooth out the video?