What is the most likely cause of a power steering pump making noise all the time?

A power steering pump making noise consistently is most commonly associated with aerated fluid. When the fluid in the power steering system becomes aerated, it means that air has mixed with the fluid, often due to low fluid levels, leaks, or a malfunction within the system. This can create a situation where the pump struggles to build pressure and circulate the fluid effectively, resulting in a whining or groaning noise. The presence of air bubbles disrupts the fluid's ability to transmit hydraulic pressure, leading to inefficient performance and constant noise as the pump operates under less than optimal conditions.

Other potential causes, while they can indeed lead to noise, typically manifest under different circumstances or might not lead to constant noise. A stuck open pressure relief valve can result in inappropriate pressure regulation, which may lead to varying noise levels depending on system loading, but it is more likely to create a different set of performance issues. A stuck closed pressure relief valve could lead to excessive pressure build-up, but again, the noise patterns would differ from that created by aerated fluid. Lastly, a slightly loose belt may cause slippage and noise, but it would usually not create a constant sound unless it was dramatically loose. In this context, aerated fluid is the most consistent and likely