Noise reduction

An axial piston machine, comprising a casing, a cylinder block within the casing, having a plurality of cylinders therein, parallel or nearly parallel to a central axis, a piston in each cylinder, a swash plate located at one end of the cylinder block and engaging the pistons projecting from the cylinders at that end of the block, mounting means for the swash plate in the casing for transmitting to the casing the piston thrusts that act on the swash plate, a valve plate secured within the casing, on which the cylinder block is mounted for rotation, a low and a high pressure main port in the valve plate, a cylinder port from each cylinder opening into the surface of the cylinder block which rotatably engages said valve plate, whereby during rotation, cylinders with outwardly moving pistons are connected to one main port and cylinders with inwardly moving pistons are connected to the other main port, a drive shaft passing through the valve plate to rotate the cylinder block, the casing having a closure member at an end which is opposite the valve plate, a cover of pliant material mounted on one of said closure member and said casing and externally of the casing adjacent to the swash plate and together with said closure member covering said end of the casing which is opposite the valve plate, said cover covering said closure member, and a quantity of air or other gas trapped by the cover against the external surface of the closure member, the natural frequency of vibration of the cover being low compared to the natural frequency of the casing.