I’m not at home for a few days, but I’m very willing to try a lot of things to get it quieter and understand precisely what’s causing the noise.
It might not be just the fan noise, because it feels like pressure.
I currently have the 580x and the lack of air vents maybe creating a lot more positive air pressure inside the case compared to the full-size MPX modules.
I wonder if opening a few of the blanking plates at the back might help?
I remove my 580x and put a wx9100 in slot 4. So basically the lower portion of the machine is empty. It's super quiet. That said, even when I left the 580x in there as well, it was still quiet. Certainly worth playing around with...