The Dreamcast is notorious for its loud operation thanks to both a loud fan and a noisy GD-ROM drive mechanism. Enthusiasts now frequently replace the fan with a Noctua NF-A4x10 5V fan, which is near-silent in operation.
In order to facilitate the replacement, a 3D-printed bracket is used alongside a 3D-printed replacement "Open" lid mechanism to allow for the proper mounting and clearance of the fan. In addition, an adapter cable with a resistor must be used for the fan to connect and send the proper fan-sense signal to the Dreamcast motherboard, otherwise the system will refuse to operate without detecting a fan.
A premade kit for this is available at Laser Bear Industries and other online stores.