As far as plant and machinery are concerned, hydraulics is a source of noise. The emergence of noise on hydraulic installations is very complex because a large number of operating and control elements working together are attached to sound-radiating mountings and walls, which act as "loudspeakers." Although individual components such as pumps and valves are already available in low noise-emission versions, it is only by contemplating the system as a whole that we can hope to achieve a significant reduction in noise.

In the case of retro-encapsulated standard power units, the individual components are frequently difficult to access and the user also has to cope with temperature problems. Modern whispering power units go far beyond conventional encapsulation because their basic design is already optimized to take account of the low noise emission factor. These modern pussyfooters are considerably more compact in terms of their construction than retro-encapsulated units. However, at the same time, all the components are still accessible and all the control and monitoring elements are arranged so that the operator can carry out checks and modifications on them externally. As far as the hydraulic installation is concerned, depending on the installed power, this means a reduction in the noise transmitted through the air of around 10-20 dBA compared with a conventional installation (pictured, Rexroth whispering power unit).