Sounds like a problem with the control for the fan, possibly the control wire for the cpu heatsink has broken or, a sensor may be stuck. try taking the casing off your laptop and checking it out you shouldn't have to remove too much stuff to get to the cpu cooler.
Also there is no such thing as overcooled, when it comes to pc's the colder the better so if the noise is not really an issue then it may be a good thing 😛