A set of experimental measurements concerning both current noise and conductance relaxation curves in CdS and CdSe photoconductors has shown the existence of a relationship between the noise power spectrum and the Fourier transform of the phototransient curve. Some of these experimental results have already been published. It appears that at least two different noise components contribute to the total power spectrum. The first component, which dominates the low frequency part of tile spectrum, is strictly related to the behaviour of the relaxation curve. Indeed, it can be attributed to the fluctuation of the photoinduced positive trapped charge and consequently of the potential barrier at the interface electrode-photoconductive material. The second component, on the contrary, is practically independent of the light wavelength, and represents an intrinsic noise component related to the generation-recombination and trapping processes within the photoconductor. In this paper we present a theory accounting for both the photoinduced and the intrinsic noise component. This theory fits well to the experimental data concerning the dependence of noise on light intensity and wavelength, using the parameters obtained from the phototransient and photoconductance measurements performed on thle same specimens. It also gives tile correct order of magnitude of the measured absolute value of the noise power spectrum.