The back plate is rattling because it is not tall and wide enough to fit the grooves in the top and bottom parts of the case. I don't know if it is on purpose because of the case moulding variations / orangepi+daughter board placement variations or who knows why. I personally installed passive dual side heatsink and made a custom back side metal grill so the hot air can escape. If you need any help regarding modeling or making custom parts, let me know. CAD/CAM is what I do. I would consider helping you design what you need for free.
Sounds interesting. What does your A600GS custom back plate look like?
