That made the system rather load on idle. On top of high minimal speed settings (like 50% for the case fan) it ignored my settings and ran the fans higher than I wanted.

Turned out the MSI BIOS fanspeed control did not work properly. However, the setup I describe above was loud until I got around to control the fan speeds properly. With that setup, the noise under load is completely defined by the gpu (a soon to be exchanged RX 570) and the noise of the system on idle vanishes with the ambient noise. Note that the H90 is only quiet when pump speed gets also reduced. I use an old Corsair H90 to cool my i5-5675C, AIO is on the front, my case has one good case fan at the back. ) + a noise isolating case against coil whine would be the be the foundation for that. A good cooler for the processor + slow running case fans + a silent psu (like BitFenix Formula, Corsair RM. How silent are you talking? Silent under load is hard, but quiet under load and silent on idle is possible without a passively cooled build.

Project mention: The minimum viable fan control script | |

Fancontrol