The “Rasping Noise” is an abnormal exhaust noise that occurs in small cars equipped with two boxes exhaust systems. It is an intermittent metallic noise that irritates the ear because of its high frequency components. It occurs during rapid acceleration or deceleration in cold conditions. Pressure signals are picked up in a critical exhaust line at Rasping conditions. Order and wavelet analysis are found to be efficient and completing tools in studying an eventual occurrence of discontinuities or shock waves in such a critical exhaust line. ©2000 American Institute of Physics.