In hydraulic power systems, variable displacement pumps (VDPs) save power, increase the productivity, or control the motion of a load precisely, safely & economically. The displacement mechanism & power-to-weight ratio of VDPs make them most suitable for control of hydraulic hybrid vehicles (HHVs). One of the problems reported from testing HHVs is that noise levels emitted by the pumps & motors are not acceptable. The lack of space, the extreme pressures and the dynamics of the pumps components limits direct observation of potential noise causing mechanisms. There are several theories as to...