When a double barrier semiconductor structure is biased near a tunneling resonance, charge can accumulate in the quantum well. Coupling between this two dimensional electron gas and the tunneling current is investigated. Experimental data taken inside a region of apparent bistability in one device reveal a satellite on the high energy side of the current resonance in the I(V) characteristic. A theoretical model based on the many-body transfer Hamiltonian formalism shows that a plasmon excitation has remarkably similar structure. Magnetic field data support the plasmon satellite interpretation.