
Straight out of the box, mine displayed the heavy ringing when switched-on.
In addition to Brian's recommendations, it seems playing with the Bias knob is most effective to minimize this phenomena's intensity and likelihood to occur; playing with [it] and the Frequency knob whenever flipping a toggle triggers [ringing]. Sometimes a few sweeps is all it takes.
Try manual-recommended setting #4 Deep intermodulation stacked behind your favorite fuzz & behold its brilliance
