The mouse did not survive interrogation. Also mouse not pictured.

I thought it was the huge heat sink that looks like it extends past the side plane of the cover. Reminds me of something I did with a CoolAir Cosmos tower. I mounted two 300 cfm fans over each CPU and took the side panel, neatly cut out the area around the fans, then 3d printed a scoop, with a slot for filtration, to fit on the side panel and allow the fans to breathe.