ZRA means Zero Resistance Ammeter and is a mode of operation of the potentiostat/galvanostat that allows the user to measure Electrochemical Noise (ECN). So ECN is not a technique but what can be measured by the ZRA technique.
Now, another question comes up; What is the difference if two identical electrodes (working and Aux) with a reference electrode were used instead of one working electrode with different aux (Pt for example) and reference electrodes.