Thanks for the inputs. Probably on my board, the case / fan configuration is incorrectly configured, so all fans run at 100%.
I tried to update the firmware to get to the chassis configuration menu. I downloaded the firmware to an USB stick (FAT32) and booted to the EFI shell.
However the EFI shell is not behaving as described in the documentation. What I get is the following when trying to read the USB stick.
When I do map -r, I get a list of block devices, not fs0, fs1 etc. When I try to change to the file system on the USB stick, I get invalid mapping name.
Surely a stupid beginner's error. Can anyone help me?