First, is the fan you bought an axial fan? If there is one, it is better to replace it with a centrifugal fan, which can reduce some noise. Second, noise elimination equipment can be installed outside the fan. If there is an air duct, the air duct and the fan must be connected flexibly, and the fixing of the pipeline should be strengthened. The iron sheet of the pipeline should not be too thin, so as to reduce the vibration of the pipeline and avoid making more noise. If possible, make another layer of sound insulation cotton outside the pipeline.