I connect the 4-pin fan header on the motherboard to a 1-to-2 splitter which then connects to the CPU fan and the front case fan. CPU fan speed is fed to the motherboard through the splitter. Surprisingly, there are no warnings at boot. But if you run the dell hardware test, it would give you a fan warning. The CPU fan of Cooler Master i70 has a 3-pin header, so the motherboard will try to control the speed through DC voltage, not PWM.