Nope, your fine. Just go into bios and disable the CPU fan warning and you'll be good. Your motherboard's BIOS is just letting you know that your CPU cooler's fan speed is below normal (for a stock cooler). Since your running a better than stock cooler, it doesn't need as high of RPM to do it's job. You can also disable PWM and let the fan run at maximum if it's not too loud if you don't want to disable the warning. All that is happening is the fan on your cooler is using PWM (Pulse Width Modulation) do control the fan RPM.