120mm + closed loop watercooling makes almost no noise. 140mm makes no noise (compared to background), but don't fit in the standard "U" format. 3U (ATX) can f

120mm + closed loop watercooling makes almost no noise. 140mm makes no noise (compared to background), but don't fit in the standard "U" format. 3U (ATX) can fit a full 120mm, but not a closed loop. 4U (ATX) take a lot of space, but the airflow and WC flow is easy to get right. I used to be a self employed embedded system (Linux) engineer and had to compile whole OS images all day long on air-gapped, on premise, systems, so I ran my own "semi-pro home lab" for a few years. Another trick is to have 5v, 12v and 48v DC lines with silent PSU like Corsair RM series directly feeding some servers so they didn't have to use an internal PSU, that leaves only the CPU and GPU as "hot" components (and the NAS, but that's another story and a solved problem). https://imgur.com/a/cGYxIPW https://imgur.com/a/cGYxIPW