A method is developed for predicting broadband noise due to the fan-wake interacting with the downstream swept outlet-guide-vanes in turbofan jet engines. It is validated against the NASA Source Diagnostic Test data. Sweep effects on the source, on the response and on the unsteady lift coupling with the duct modes are discussed. The mechanisms of broadband noise reduction due to vane sweep are studied, and a simple model to account for sweep effects is proposed accordingly.