I have a Nvidia 5090FE and there is a bug with how it runs where sometimes it will switch its fans on and blast one of them at 2000 RPM for a few seconds.

It's a compounding of poor tweaking parameters for the system. The GPU tends to warm up on its own and reaches a temperature threshold and turns on the fans at the minimum speed of 30%, which is pretty loud for some folks, not me, but then there is this bug that makes it so 5 to 10% of the time that this happens, it blasts a fan at a speed that is very loud and disruptive.

The hack I'm going to perform to alleviate this issue without attempting to fix any of it, is to augment the cooling with the GPU in fans-off idle mode with an extra 92mm case fan that's always running. That way when the fans are off, this small amount of extra airflow present will keep the GPU cool enough to more or less consistently leave its fans at 0 RPM. Since I run 240hz monitors I suspect that I might even need even more than a single 92mm fan so I may also consider a slim 120mm fan.