BACKGROUND: Noise at production site or at any other place where technical equipment operates is a huge issue. It has a strong negative effect on human nervous system, reduces average lifespan and causes a number of severe diseases. That is why reduction of noise, produced by pumps, is one of the current priorities of hydraulic engineering. AIMS: In this study, the experimental research of sound transmission through an operating pump and a non-operating pump was carried out. The aim of the research is to find out, whether the last stage of a multistage pump is the main source of hydrodynamic noise (HDN) in pressure line (or the first stage in suction line), or all stages somehow contribute to HDN. METHODS: The experiment was carried out on the TsN-2 two-stage impeller pump. In order to generate a sinusoidal signal, an imbedded generator, a vibration test rig and a power amplifier were used. Data acquisition for measurement of HDN and vibrations was performed with use of a conditioning amplifier, a hydrophone and an accelerometer. A 4-channel spectrum analyzer served as a device for processing the studied signal. In addition, a theoretical calculation, considering some physical assumptions, was carried out in order to obtain a more general and accurate concept. RESULTS: After completing the experiment, hydrodynamic noise levels and differences for three cases were obtained. These cases are for the switched-on pump, the switched-off pump and for the pump with the removed stage. The data obtained with hydrophones (hydrodynamic noise levels) was correlated with the data obtained with accelerometers (vibration levels). As the correlated data analysis result, the sound insolation distribution over the spectrum was obtained. CONCLUSIONS: According to the study results, it can be concluded that the absence of one of two stages ambiguously affected on the sound-insolation properties of the pump. Moreover, no firm conclusions can be drawn about the pump operation influence on the change in its sound-insolation properties.