Abstract: A containerised generator set comprises a generator arranged within a container having a first aperture through which cooling air is exhausted in use. A pair of first doors are arranged to pivot outwardly on either side of the first aperture, with a removable wall being removably mounted between the first doors and spaced apart from the body of the container by the first doors from its lower end region to its upper end region in its mounted position. The removable wall and the first doors define an exhaust air duct which preferably includes a sound absorbent material. The exhaust air duct extends for at least most of a total height of the body of the container to attenuate noise from the generator. Exhausted cooling air flows upwardly from the open upper end of the exhaust air duct and away from the immediate operating environment.