Rail vehicle (1) having rail wheels (3,4) accommodated to guide the rail vehicle along a railway track (2) and said vehicle comprising means for detection of a flaw or flaws in the railway track, wherein the rail vehicle is provided with a noncontact vibrometer (9,10) which is arranged to measure vibrational movement of the railway track surface.Precision and Microsystems EngineeringMechanical, Maritime and Materials Engineerin