I buy my PCs in big tower cases with easy to open doors. That way even I can do minor maintenance operations, like changing a graphics card. So I looked into the computer while it was running, and quickly identified the problem: The three fans on the heat exchanger of the water cooling unit were making the noise. And when I looked at my CPU temperature, it was below 30°C, which even I know is unusually frosty. And little by little I figured out what the problem was: The fans on the water cooling heat exchanger had been running at 100% capacity for two years. Which A) is unnecessary, B) makes the fans louder, and C) causes a lot of wear on those fans.

So first step, I replaced the Xilence fans, which I suspect aren't particularly high quality, with new fans from Corsair, bought as a set of 3 for just $20. That eliminated the part of the noise that was caused by the old fans now scraping against their frame. While changing the fans wasn't very easy, I just about managed, and at the same time could clean the heat exchanger and ventilation of my PC from two years of accumulated dust. The main problem was that the old fans each were separately connected with long cables, while the new fans had short cables and needed to be daisy chained.

Now the computer was back up and running, and the CPU was even cooler, as low as 26°C when just running Windows and Chrome. Then I looked into software for controlling the fans. With the MSI Center software for my motherboard I had a lot of problems. So in the end I decided to set things up directly in the BIOS. While I couldn't find the controls for the LED lighting of the fans, that wasn't really that important. What I did find was how to set a curve how fast the fans should be running as a function of the CPU temperature. That worked like a charm: My computer is now very silent, and still has a CPU temperature of just over 30°C. When I run a game like Baldur's Gate 3, the fans audibly speed up a bit, although still less than the noise they made at 100%, and CPU and GPU temperatures stay below 60°C.