A new adaptive "beamforming" signal-processing algorithm is developed to locate the loudest noise sources aboard a railcar that passes by a trackside immobile microphone array. This proposed microphone-array beamformer tracks the railcar's spatial movement with the aid of two inaudible acoustic beacons placed aboard the railcar. The proposed scheme then localizes the noise sources with reference to the railcar's coordinates. No auxiliary infrastructure (e.g., no radar or video camera) is needed besides the onboard beacons. Monte Carlo simulations and anechoic chamber experiments verify the efficacy of the proposed scheme.Department of Building Services EngineeringDepartment of Electronic and Information Engineerin