In the present work, we will discuss the vibration spectrum impact of water and sand inside a railway container. To do so, a scaled model of a container car was driven on tracks with three accelerometers on its side to record the container response. The experiment was conducted with three different water fill levels and two sand masses. As the data given by the accelerometers was recorded in an ambient vibration environment, the random decremental technique was used to determine the system’s free vibration response. Then the wavelet transform was applied in order to obtain the modal parameters of the structure. The results were then compared to draw conclusions on the effect of water and sand on the tank.