Electrical circuit where two or more paths to ground (true 0 volts) have different voltages as a result of current flow through wiring or chassis elements. The minute voltages on some ground legs may find their way into equipment input circuits and be amplified, causing hum, buzzing or in the worst case, inaudible high frequency oscillations, sometime at high power levels, that can ultimately cause destruction of tweeter voice coils or even burn out amplifiers.