If you have an AMD GPU and installed their latest drivers (Crimson), there's a bug that turns off the automatic fan speed adjustment in the OverDrive settings. In my case it locks it at 25%. Apparently this resets every time you boot your machine. So until it is fixed, make sure you switch it every time you boot or start a game.
I use(d) MSI Afterburner to set a custom fan profile, but the driver seems to override it.
Bring up the driver settings (right click on desktop, should be at the top) > Games > Global Settings > Global OverDrive > Fanspeed to off (i.e. automatic).
Everything's in German here, but the layout will obviously be the same:
