Flow-generated noise generated on the quiet side of the primary attenuators of a ventilation system is the result of interaction between air flow and duct discontinuities. It is of engineering importance to predict the flow-generated noise caused by air duct elements in ventilation systems at the design stage. However, all prediction methods are based upon an isolated in-duct element that is very different from a real ventilation system. Until recently, Mak and Yang have produced a prediction method for flow-generated noise produced by the interaction of two elements in air ducts. In this paper, an attempt has been made to modify their equations so that their predictive equations can possibly be used to predict noise produced by “real” duct discontinuities. By comparing their predictive values with the experimental results of Oldham and Ukpoho, their validity can be proved. The modified Mak–Yang predictive equations, therefore, provide a basis for permitting a more accurate prediction of flow-generated noise produced by various configurations of two in-duct elements and duct dimensions.