We do a lot to make your small rotating noisemakers in the PC case more silent.
In addition to sound insulation and decoupling, there are more ways to achieve this.
Or just install a fan controller to pulse the fan voltage or reduce the fan voltage.
The air flow is then usually still enough for a good cooling, but the volume of the fan is massively reduced.
The offer on the PC market is manageable, and controller starts with simple 3 step types, followed by LCD, LED, or VFD Display to the top fan controllers with touch screen and remote control via Internet.
Today, we test such a fan controller - the Lamptron CM615 6-channel fan controller with touch screen display.