Fan eating CPU

I just bought a new computer and everything runs fine but I've been noticing that after the case fan gets to a certain temp the fan starts whirring at full blast and all of a sudden the System process goes up to almost 99 CPU usage. So my question if this, does a case fan use the CPU to sense the temperature in the case and thus eats it away? And if so, is there a way I can disable that function and just have the fan be a full blast all the time?

You probably have some fan speed controlling software that has gone bad.
It might also be some stupid form of temperature regulation where the SYSTEM sends NOOP instructions to the cpu in order to lower the temperature.

But it would help if you could tell us what cpu you are using, if you know of any fan controlling software and what computer you are using.