This chapter is devoted to the backward noise and parasites. Noise is a highly prominent and stochastic phenomenon, but from the other point of view, parasitic effects can be determinist effects in the three dimensional (3D) integrated circuit design. Noise is a universal phenomenon. Generally, micro-electronics and, of course, nano-electronics are domains where autonomous noise sources can be dependent on each other due to their proximity. The chapter introduces the concepts such as correlation of random variables, and noise spectral density. It briefly reviews the concept of transfer impedance; calculations at the one-dimensional level have already been developed, but there are few in two dimensional and nothing relevance in 3D. Digital noise can affect analog parts of the circuit. Substrate noise involved in by the digital part will degrade the performance of analog circuits. The chapter describes the Markovian stochastic algorithm.