An inspection method and system that locates a probe proximate a region of a shaft that is welded to a slug that secures the shaft to a housing. An acoustical wavefront may be emitted from the probe into the shaft toward the slug, and a reflection of the acoustical wavefront may be received with the probe. Whether the reflection occurred at an interface between the shaft and the slug or at a distal end of the slug is determined based on a time that the reflection is received by the probe.