I have a 2005 C240 4matic sedan with 76k miles
I am getting a loud engine whining noise at start up that slightly dies down when engine is warm. But when in "park" and any amount of gas pressure is applied engine whine gets louder, even when in drive there is loud whine all through the gears... Just replaced the power steering pump two days ago and noise didnt go away... any one else experience this annoyance or have any suggestions to try? any ideas Please!!

Did you bleed the power steering system?

System was bled... and new fluid was used...I read something about a belt tensioner shock or tensioner damper.... think that could have anything to do with it?

actually you can scratch my previous answer about the belt tensioner... the belt is not sqeaking... it is definetly a noise that you would expect out of the power steering pump.... arrgghhh.... I just replaced that freaking thing and no help...

Did you replace the reservoir? it has a built-in filter.

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Are you sure the P/S is the source of the noise???The pulley on the A/C compressor may be the problem. When they fail, the sound is very similar to a P/S type noise. The way we diagnose this at the dealership is to install Poly V-Belt #011-997-96-92, or it's equivalent. This belt is shorter than the original, and can be installed in such a way as to eliminate the A/C compressor from the loop. If the noise goes away, the A/C pulley is the problem.

Thank you thank you for all of your advice Gents!! I will definetely give that a try and let you know of my findings... I am hoping that the AC is ok cuase i doubt that will be a cheap repair.... arrrgghhh