A neuromodulation system configured for providing sub-threshold neuromodulation therapy to a patient. The neuromodulation system comprises a plurality of electrical terminals configured for being respectively coupled to a plurality of electrodes, modulation output circuitry configured for delivering electrical energy to the electrical terminals in accordance with at least one modulation parameter, thereby providing therapy to the patient at a sub-threshold level and control circuitry configured for controlling the modulation output circuitry in a manner that pseudo-randomly varies a value of the at least one modulation parameter based on a previous value of the at least one modulation parameter, such that the delivered electrical energy is continually maintained at the sub-threshold level.