A study on pseudoshock dynamics in low enthalpy, non-reacting supersonic flow was experimentally conducted for both axisymmetric and rectangular supersonic combustors in the ACT-II facility. In both cases, the choking was produced by means of mass addition via inert gas injection at the combustor location. The aim of the experiments was the investigation of pseudoshock dynamics in the isolator of scramjet engines within the transition regime. The experimental methods used in this study was flow visualization obtained using high repetition (10 kHz) CO2 Rayleigh scattering coupled with simultaneous time-resolved pressure measurements. A comparison between the pseudoshock dynamics in the axisymmetric and rectangular scramjet geometries was made. It is revealed that the pseudoshock exhibited different behaviors in the two geometries: the pseudoshock in the axisymmetric scramjet was found to exhibit regular periodic oscillations at a single location in the isolator, whereas the pseudoshock in the rectangular scramjet did not stabilize at a single location. Furthermore, the pseudoshock in the axisymmetric isolator maintained a 2-dimensional structure throughout its periodic motion, while the pseudoshock in the rectangular isolator manifested in a 3-dimensional structure at different phases of its advancement. This 3-dimensionality was found to be a result of the interaction between shocks originating from the sidewalls with those from the top and bottom walls. This discrepancy in pseudoshock dynamics was attributed to the acoustic mechanism of the choking process, specifically how the choked subsonic flow downstream influences the unsteady motion of the pseudoshock through the boundary layer.