The noise generated in a hydraulic system occurs in three forms: audible sound, structural vibration, and fluid pressure pulsations. The selection of quiet pumps, although an important step, does not necessarily quiet the operating system. The elimination of entrained air in the system fluid may not remove the problem. Frequently, a tradeoff of operating parameters in a pump or motor is the best means of noise control. Installation practices are important and may require isolation of the pump or motor assembly from the rest of the machine structure.