Multiple reflections at cell walls give rise to modulation terms in the transmission coefficient of the beam passing through a spectrophotometric cell. Considering the cell as a planar layered system, these intrinsic modulation terms are subjected to numerical simulation according to a multilayer structure theory, assuming the system behaves as an infinitely thick medium contained between two layers that act as multilayered systems, which is approximated by a three layer system with a thicker second layer for simplicity. A frequency modulation is used to correct for lack of parallelism in cell walls. The degree of coherence of the incident beam is taken into account in the squared magnitude of the Fresnel transmission coefficient. The modulation pseudoperiod and an inner pseudoperiod are estimated, and noise in the average transmission signal due to intermodulation is explored.