I have a similar problem to the many described here. My microbrute plays the tone of the last key I pressed (continuously, even after the key is released, until a different key is pressed) when all the oscillators, filter, resonance, etc. are set to zero. It's worse in the headphones and when the volume knob is set between 1 and 3 o'clock. It's not hum or noise. It's a tone, and its pitch can be modulated by the LFO, although changing the position of other controls besides the volume and LFO does not affect it. I didn't expect to get a perfectly quiet machine for $300. My Monotrons, for example, hiss and hum a bit. But this is different and quite distracting. I like the Microbrute a lot otherwise, but I'm disappointed with this defect, which seems to be quite common from what I've read on this forum.