Recent efforts to address microprocessor power dissipation through aggressive supply voltage scaling and power management require that designers be increasingly cognizant of power supply variations. These variations, primarily due to fast changes in supply current, can be attributed to architectural gating events that reduce power dissipation. In order to study this problem, we propose a fine-grain, parameterizable model for power-delivery networks that allows system designers to study localized, on-chip supply fluctuations in high-performance microprocessors. Using this model, we analyze voltage variations in the context of next-generation chip-multiprocessor (CMP) architectures using both real applications and synthetic current traces. We find that the activity of distinct cores in CMPs present several new design challenges when considering power supply noise, and we describe potentially problematic activity sequences that are unique to CMP architectures.