RPM fan control question.

Well, the cpu cooler operates from 1600rpm to 2200rpm, witch I control by speedfan.

The thing is, if the PC ambient temp is higher than 30c, the fan stuck at 1700rpm witch makes an annoying noise that otherwise don't if it is at 1600rpm.

If the ambient temp of the PC is lower than 30c always stays at 1600rpm.

I don't get it, should the motherboard have some option to fix this?, because at summer the PC amb temp will always be at +30c....(also, from 1600 to 2200 only -2c improvement is in place so I don't need it at full speed)

The cpu cooler is properly installed, the pins etc...

Motherboard : asus maximus formula
Cooler : asus arctic square(not that is relevant but..)

I already posted on cooler section, asked a mod to move it but so far with no avail, so I'm trying here as the noise is too annoying and can't stand it.