The main noise source in gas distribution systems is the gas pressure reduction in regulators. Nowadays the special mufflers, representing a set of orifices, are widely used for pressure regulator noise reduction. However, the installation of such devices may cause malfunction of the unit. That is why there is a need to study the characteristics of regulator with the muffler in order to select the parameters at which the desired pressure reduction is retained and the noise is reduced.This paper studies the regulator which represents an equivalent of reduction valve of a similar scheme with the muffler installed in the outlet line. The output impedance increase may lead to loss of stability and control accuracy. The mathematical model of this system was implemented in the Simulink software in order to analyze the muffler impact on pressure relief valve static and dynamic characteristics. The program in Matlab software was also developed for determination of the noise generated by the system. The experimental research using the pneumatic bench was carried out for mathematical model verification.The dependences between the main system operating parameters and the muffler flow area were obtained as a result of simulation. The muffler influence on the transient processes quality was analyzed. The areas of stability in the regulator and muffler parameter space were calculated. The muffler flow area values, providing the lowest level of the noise generated by the system were determined. The theoretical results have good correlation with experimental data.