The devices capable of producing some sound inside a normal laptop are the fan and the hard drive. When the fan is not attached properly, due to some screw or broken part, then there will be reasons for noise. In the case of the hard disk, this only makes a noise when tired.
'''Solutions:'''
- securely fasten the fan and make sure that all the connectors are secure;
- remove the hard drive and check if the noise continues;
- disconnect the fan connector and check if the noise continues;