This paper deals with the stability of a plane interface between two different superposed fluids moving through two different porous media. The system is acted upon by an alternating electric field parallel to the interface. In addition, the influence of mass and heat transfer is taken into consideration. The boundary-value problem contains the linearized equation of motion together with nonlinear boundary conditions. It leads to a nonlinear characteristic differential equation governing the surface evolution. This characteristic equation is accomplished up to a third-order. It has periodic coefficients. The method of the multiple time scales is applied to a one-degree-of freedom system with quadratic and cubic nonlinearties subjected to parametric excitations. This method is used to determine the modulation of the amplitude as well as the phase. The steady state solutions and their stability are investigated. Previous relevant works are references. New and interesting properties of the solutions are derived. For example, we found that a softening behaviour causes a significant shift in the primary resonance frequency and the solution loses stability. Effects of different parameters such as: the damping factor, the coefficients of nonlinear terms and the amplitudes of the parametric excitations of the system are numerically investigated. It is also found that the response peak decreases with the increase and decrease of some parameters. The response amplitude will be contracted and becomes oval for increasing and decreasing parameters. The response amplitude loses stability with the varying of the parameters. In the case of sub-superharmonic resonance, the steady state response of the system shows a hardening behaviour in most cases for the chosen parameters although the physical nonlinearity of the system is of the softening type. The response amplitude loses stability with the decreasing and increasing of some parameters.