Hello, I'd like to give some insight about this matter. I've tried to unplug, press "save" while pluging back / choosing guitar instead of USB. It doesn´t work for me, but once you are in that mode, if you move the treble knob it allows you to choose the "z setting". It looks like the z setting has something to do with impedance. As soon as I choose a different value (can't remember now what exactly) the problem is solved. BUT: once I unplug and restart the pod the change in the z setting is lost and stops working again.
I'ts curious that if I connect a booster pedal (a real one) before the pod it kinda works... not very well though
I'm returning this unit and not buying any hd pod 300 or whatever ever more. Just wanted to give you my two cents.
Cheers!