Probe systems and methods for testing a device under test are disclosed herein. The probe systems include an electrically conductive ground loop and a structure that is electrically connected to a ground potential via at least a region of the electrically conductive ground loop. The probe systems also include nonlinear circuitry. The nonlinear circuitry is configured to resist flow of electric current within the ground loop when a voltage differential across the nonlinear circuitry is less than a threshold voltage differential and permit flow of electric current within the ground loop when the voltage differential across the nonlinear circuitry is greater than the threshold voltage differential. The methods include positioning a device under test (DUT) within a probe system that includes an electrically conductive ground loop and nonlinear circuitry. The methods also include selectively resisting and permitting electric current flow within the ground loop and through the nonlinear circuitry.