This report covers analytic and experimental gasdynamic studies relevant to stability issues of the scramjet supersonic combustion chamber. Its intended purpose was to search for small amplitude very short time scale precurser signals which eventually grew into combustor flow instability, but at a much longer time scale than the signal itself, and consequently offer possibility of control before amplitudes got out of hand. The experiments were done in a basic 2.5 Mach number stream with an artificially thickened boundary layer corresponding to the ingested ramp boundary layer that occurs in the usual installation . A disturbance produced downstream by a small shock tube discharging normally to the gas flow successfully disgorged the shock structure; time resolved pressure and Schlieren image records were obtained. Because upstream signal propagation through the subsonic boundary layer of a supersonic flow is seen as an important issue in the phenomenon under investigation, a rudamentary analytic model was developed. It consists of an acoustically compact element, in which mixing and heat release may occur, with long constant area ducts upstream and downstream of this element. It employs a two stream one dimensional approximation, the main supersonic stream and a subsonic second stream representing the thick boundary layer. Conditions under which interfacial disturbances may be propagated upstream are examined through several examples.