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I have diagnosed the grinding or metallic noise coming from the front of engine as coming from the ABC pump. I have replaced all the plastic pulleys and bearings in the metal pulleys (my car is an S55 so I did replace the supercharger pulley with a slightly smaller 88mm pulley). My ABC system does not show any leaks and when I performed a rodeo test it appeared to be within suitable pressure ranges. There are no visible leaks from the pump area and the reservoir is holding the same amount of fluid. I tried replacing the pulsation damper with a brand new Mercedes part to see if that would remedy the problem and while it did seem to improve the ride quality some, the noise did not really subside. There are no errors appearing on the instrument cluster and I should point out that this noise only is at idle and will go away even if I turn on the air conditioning while the car is running at idle. I did think it was the a/c due to this strange interaction so I even replaced the a/c clutch or whatever the Denso unit uses. When I took all the belts off and ran the car for about twenty seconds, there was no noise at all so that's how I figured it had to be that ABC pump.

*Edit - A buddy and I both listened to the pump with a mechanics stethoscope and it clearly sounded as if the noise was originating from there.

tusabes

It will need to be replaced at some point , question is do you want to replace now or wait till it fails on you

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I should have mentioned that I recently purchased the car and the previous owner stated that he had put in a new (likely remanufactured) pump about one year ago. I have been looking around online and it appears that new pumps are not even being sold. Even the pumps from Mercedes are listed as remanufactured. Do you know what the source of the noise is inside the pump?

wallyp

I would investigate a used pump.

Alpina7

post a video let us hear it

CaptainR

My 05 s55 with 56k on it does the same thing and I hope to god its not the ABC pump. Noise goes away with the A/C on....

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I will post a video asap; I am waiting for a pulley that USPS has somewhere in the ether. It's an updated version of the metal double idler pulley and when I replaced the bearing in mine, I was getting bearing float. So I don't have the belts on my car right now...

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I just replaced the serpentine belt as I accidentally stepped on the one as it was on the ground and it has some cracks in it so it broke along the cracks. With the new one on, the noise has quieted down a bit, but I am still waiting on a new pulley...

*edit - I am running it with the old double idler pulley with the replaced bearing which I am still getting bearing float.

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CaptainR

Sounds exactly like mine, I thought it was the AC pulley but the noise went away whenever I turned the air on. I wonder if the pump itself is going. I did a complete suspension system service and it didn't change anything. I really have not messed with mine as I only pull the car out to drive rarely anyways. I hope you get it sorted out paste.
Chris