A hard object or stone detection method and apparatus for detecting and removing discrete hard foreign objects from mobile agricultural equipment, particularly an agricultural harvester (1) including apparatus (12) for providing a flow of cut crop material to an elevator (21) for delivery to a threshing system (3). The apparatus includes a foreign object detecting mechanism (35), including a foreign object detecting circuit (42) for detecting foreign objects and an object exclusion or rejection mechanism (44) operationally connected to be activated by the detecting circuit. The detecting circuit includes at least one vibration sensor (40) operable for outputting a signal (I1), and a combination of a high pass filters (140) and frequency bandpass filters (52, 152) and variable threshold comparators (54, 154) for processing the signal along first and second signal paths, and at least one microprocessor (60) or microcontroller including a pulse rejection network. The microprocessor can be electronically connected to control the threshold comparators and programmable amplifiers, and activates the object exclusion or rejection mechanism when the pulse rejection network generates an internal signal indicating presence of a hard object.