Sound is a compression (mechanical) wave in a gas or liquid. Significant noise can be induced by a vibrating solid in either a gas or liquid system, typically through bending waves. Conversely, noise in a fluid can induce vibrations in a solid. The most obvious examples are speakers and microphones. However, a similar interaction occurs when a pipe wall or enclosure wall vibrates. Station piping noise will be a combination of how the pressure waves within the fluid (produced by turbulent flow or a compressor excitation) reflect upon the internal piping structure and how these waves induce vibrations in the solid pipe wall