Have you tried one ram stick in each ram slot one by one?
Please also refer to the following links for RAM q-led and no display.
The fans rattle you mentioned is cpu fan or chassis fan?
Please test with minimal components.
Also, if you have replaced the ram and the motherboard, the yellow dram q-code is still on, it also indicates the cpu error.
Have you checked or replaced other cpu?
For q-code A5, it might be caused by the peripherals. Please remove all peripherals and test with minimal components.
For internal fans rattle, could you please send RMA again for further examination?
May I the serial number and the RMA number after sent RMA via PM?