The laptop fan is always running
If cooling fan in your laptop is always running, it could be that the hardware that controls the cooling system in the laptop is not very well supported in Linux. Some laptops need extra software to control their cooling fans efficiently, but this software may not be installed (or available for Linux at all) and so the fans just run at full speed all of the time.
If this is the case, you may be able to change some settings or install extra software that allows full control of the fan. For example,can be installed to control the fans of some Sony VAIO laptops. Installing this software is quite a technical process which is highly dependent on the make and model of your laptop, so you may wish to seek specific advice on how to do it for your computer.
It is also possible that your laptop just produces a lot of heat. This does not necessarily mean that it is overheating; it might just need the fan to run at full speed all of the time to allow it to stay cool enough. If this is the case, you have little option but to let the fan run at full speed all of the time. You can sometimes buy additional cooling accessories for your laptop which may help.