A study of the Relative Intensity Noise (RIN) of an optically injected semiconductor laser is presented versus the injected power. The seeded laser is then operating from an amplifying regime towards a locking one, at the same wavelength than that of the master one. It is shown that when the Master is more coherent than the slave, a reduction of the RIN of the slave is progressively observed along with an increase of the injected power. In the converse case, no significant modification of the RIN is experimentally observed.