What is the temp. of the CPU? That is the real question. If the CPU is hot you need to increase the fan speed. That can be done in the BIOS.
Idle CPU temp is right around 30 give or take 2 degrees...Load temps shoot up to 58-65 or so
In general, silent fans don't spin very fast ("silent" 120mm fans between 900 and 1500), even less the larger they are. There are exceptions, ofc, as there is to everything.
1040 RPM is a little strange though, as fans mostly spin at increments of 100, like 700, 900, ... 1600, ... Sometimes of 50, but I've never seen a 40.
So I guess it's regulated by your motherboard. Check if it's a PWM fan (4pins, not 3), that could explain the regulation and still report as a 100% speed setting.
Also check if the fan faces in the correct direction: blowing air out of the case, not into it.
It's actually anywhere from 1017-1021. Not the 1040 I reported earlier...just checked again.
The Fan is 3 pins...connected to the Pwrfan 3 pin connector on my MB