Interconnects have deserved attention as a source of crosstalk to other interconnects, but have been ignored as a source of substrate noise. In this paper, we evaluate the importance of interconnect-induced substrate noise. A known interconnect and substrate model is validated by comparing simulation results to experimental measurements. Based on the validated modeling approach, a complete study considering frequency, geometrical, load and shielding effects is presented. The importance of interconnect-induced substrate noise is demonstrated after observing that, for typically sized interconnects and state-ofthe-art speeds, the amount of coupled noise is already comparable to that injected by hundreds of transistors.