Transient sidewall mass addition is one source of acoustic disturbances inside the chamber of solid rocket motors. If not properly accounted for in the design stage, resonance can occur which can lead to motor failure. This paper presents preliminary work on the numerical simulation of the acoustics in a two-dimensional slab motor using a high-order accurate, low-dissipation numerical solver. For verification of the numerical solver, we compare solutions to Culick's solution for constant injection, and to the results of Hegab and Kassoy (2006) for a space- and time-dependent injection. In addition, we present preliminary results when the injection boundary condition is described by a linear response function, or by velocity-temperature temporal correlations defined by a propellant mor-phology. In the latter case we show that the morphology strongly affects the amplitude of the longitudinal acoustic modes.