There may be several reasons for noise in power steering booster system. Some of them are connected with the fluid. If the fluid is dark, has contaminations, it needs to be changed simultaneously with the system cleaning. Roaring may occur because of incorrect tense of the driving belt. This problem can be eliminated by correct adjusting. The flow regulator valves and the oil seals defects are rarely observed, and also lead to noise level increase during operation though. In this case the defected parts need to be replaced.
The most common reason for roar is friction parts wear in powers steering booster system.
Bearings wear can be diagnosed by looseness or irregular rotations of the pump runner. Before that the driving belt should be taken off.
When the noise in the system is caused wear it can be eliminated by applying Revitalizant ®