The Plexi is actually particularly bad for it - http://www.box.com/s/1f17246c80e1917d941f All models are affected by this, but not equally. In some it's easier to dial it out by changing the Bias than others. This leads me to believe it's not a hardware issue, though it may be somehow influenced by it(and this is my second unit anyway). You can hear it particularly badly when I pick the lower notes. As awesome as the mid gain sounds are, especially now with the cab controls, I feel like giving up on the unit now, maybe going back to an M9(though that had some of it's own problems).