My car has done this for a while. 2014 GT, stock clutch, stock driveshaft me shorter. Only does it under braking, worse under hard deceleration from higher speed. No grinding when shifting in any gear, shifts smooth. Never experienced any lockout when shifting at high rpm. Had to speed up and stab the brakes a little harder to get it to do it, which is why there is a cut in the video as I stopped recording and then started back a few minutes later. Anyone ever heard this noise before?