What exactly is a thru axle? I've never thought a bike was flexy except one time I had a Mag 21 with the pressure unequal between the the fork legs. However, bike manufacturers concluded that bikes flex at unusable levels ten years ago and now you've got to elaborately screw your wheels in. I can even take the wheels off this dumb bike without a hex wrench. All these complicated screws and crevices are how the derailleur hanger attached. Well, I removed the rear wheel and heard the same creak when reattaching it! It was somewhere back there, but buried deep within the removable thing that is the threading for the thru axle as well as the derailleur hanger. The creak was coming from that and after months of fighting the noise, a little grease fixed it. None of this would have been necessary with a quick release.
