Aeroacoustics have become increasingly important as they significantly determine comfort in passenger compartments. Electric vehicles typically feature an underbody designed to minimize drag. The aerodynamic design also contributes to a reduction in acoustic interference. However, low frequency pressure fluctuations with significant amplitudes in the range of 30 Hz have been observed as a result of the optimization. Time-resolved Particle Image Velocimetry (PIV) measurements in the flow field beneath the car already showed periodical structures around the dominant frequency. The aim of this study is to show the correlation between flow characteristics and low-frequency pressure fluctuations in the interior. A mobile measurement system was established to simultaneously acquire acoustic data and velocity fluctuations near the underbody using hotwire anemometry. Direct online processing of both data streams enables a precise quantification of the mathematical correlation between acoustic and aerodynamic signals. Relevant flow phenomena were detected beneath the vehicle by pointwise traversing the hotwire probe. Additionally, visualizations of the wall shear pattern along the underbody showed a strong correlation with measured results and provided further insights into the underlying flow physics. It is demonstrated that a combined application of quantitative and qualitative experimental techniques, as well as simulations, provides a deeper insight into the underlying mechanisms, thereby enhancing the understanding of the complex flow field. Finally, this approach facilitated the development of countermeasures in the early stages of development, reducing the need for unplanned optimization loops.