The unsteady shock train dynamics under the influence of upstream shock-turbulent boundary layer interactions have been studied using experiments carried out in a constant area isolator having large span to height ratio. Measurements of the pressure distribution in front of and across the shock train have been recorded using a pressure scanner and the dynamics of the shock train are analyzed using high-speed shadowgraph imaging and time-resolved static pressure measurements. Firstly, an analysis of the shock train oscillations without the effect of upstream disturbances was conducted and the shock train was found to oscillate periodically at frequency less 100 Hz. It was observed that the separation due to incident shock upstream of the shock train has a significant impact on the shock train dynamics. The periodic nature of the shock train oscillations are modified with the introduction of upstream perturbations. The spectrum of dominant POD modes also agree with that of the pressure measurements.