1999 ML430 120K miles

I just replaced the power steering pump including the reservoir with no change in the whining noise. Somewhat disappointing but a good price on the new pump and doing it myself helps. My guess at this point is that a bad hose is causing the pump to whine. The hose internal lining could be collapsing possibly and restricting the flow of fluid throughout the system?? I am taking it in to the dealership for the return hose to be replaced via the bulletin. The return hose popped off the other day when it was cold outside. The end of the hose looks like mush, maybe a hint at what the rest of the hose internals look like.

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99 ML430

I just had the power steering hose replaced via the Mercedes service bulletin and sure enough the power steering pump whine noise stopped. This is proof (to me) that the hose itself can be bad and cause the power steering pump to whine. Before the hose was replaced the power steering pump would whine once it warmed up (exactly opposite of the more common symptoms). I assume this is due to the bad hose restricting the flow of fluid somehow.

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99 ML430