BIOS fan settings D54250WYK

Hi,

I can't understand how the BIOS fan setting is working on my D54250WYK.

With the BIOS defaults the fan spins constantly (regardless of load) loud at 3000rpm. If I change the only parameter "duty cycle" from 40 to 20 then the fan spins much more silent at approx 2000 rpm. There are no settings for cool, balanced or quiet mode (?).

Is there any documentation on the fan settings for D54250WYK?