Has anything happened to your laptop recently prior to the noise that you started to hear? Has been there any power outages in your area these days? My advice is to bring the laptop to a PC technician, because the damage of it could be more severe than a failing fan. There could be a problem with your hard drive. If the noise that you hear comes out from it, it means that the HDD has a physical issue and cannot operate how it should be. You may need to use the service of a data recovery company to get the data back from the drive.