Ok, I've talked to my service advisor about this a couple of times, and he's even done a ride-along.

Shortly after I bought the car, I started to hear a "squeeking" sound from the right-rear area. I've gotten no brake-wear indicators, and I'm not hearing the audible brake-wear indicator either. It doesn't sound like a wheel bearing either.

My SA claims that it's common for the charcoal filter, that is in-line with the fuel line, to make this sound. He said that this is a common issue, and many people have commented about it on the W203.

Lately it's becoming more and more constant, and louder...

Have any of you experienced this too? Am I just going psycho? Think it's something else? Think I need to hound my SA some more?

 

Chris,
This is news to me - my car does no such thing - just home from a long run and marvelling at how quiet the car is after 5 years - zero tyre noise on Michelin Exalto2's - zero creaks, rattles or other noises. - perfect. And there is nothing wrong with my hearing.

Sounds like I'm prepared to be proven wrong but...?????

 

Id put $$ on the rear sway bar bracket bushings... They start out quietly and progressively get worse and worse. They can eventually making creaking and loud cracking sounds. Ive found out the hard way. Buy a <10 dollar tub of silicone grease and lube up the sway bar brackets bushings.

 

Tru - I'll put money on you being correct!!

 

Ok, I can totally do that. Next question is...where do I find that? LOL Can I get a diagram or a picture?

 

You cant miss them. They are the two brackets that attach rear sway bar to the body of the car... They are right behind the under body panels. Someone w/ diagrams (splinter!) could probably chime in, but im sure there are lotsa pix out there.

 

BTDT.

If it (#20) is the source of the noise, might as well replace the pair while you’re doing it.



Part number:

203 326 00 81 for the standard suspension

203 326 08 81 sport suspension (code 486)

 

I have to make one other comment...which makes me wonder if it is the bushings...I hear the noise when I'm not even moving as well.

If the car isn't moving, then can the bushings make noise?

 

I dont think the bushings can make noise w/o moving... okay, lol i give up.

 

Is it even true that there is a charcoal filter in line?

Makes me wish I had my Accord still. I got to know that car so well. I'm still learning about my baby!

 

If charcoal filter == fuel filter. Yes.

 

And the fuel filter is located in the right rear of the car?

I've never heard of a filter squeeking. Think it might need to be changed?

 

Oops! not likely - that puts a different complexion on things - Are you sure it's not just the ringmain pump running? One man's squeek is anothers buzz. Can you still hear it running for a few secs after shut down? My car does that but it's just the pump & normal.

 

What does the ringmain pump do? Is it a higher pitched sound?

I'm in full-on ignorance mode here.

 

It is one of the Service Advisor’s primary responsibilities is to ensure problems are properly diagnosed and rectified...in concert with his technicians. That is their job. Since he claims it’s “common to make that sound”, ask him respectfully if MB has issued a DTB (diagnostic technical bulletin) to address the situation. It should not be considered normal, simply by the fact they don’t all do it.

Our cars do have a charcoal canister that absorbs evaporative hydrocarbons that would otherwise escape to the atmosphere from the fuel system…to be burned when the engine is running. There are valves and fittings associated with it, but they and the canister itself are not known for their proclivity to make untoward noises.



Let’s see if you can get this ironed out before you feel compelled to shop for another Honda.

 

Trust me, this Benz is being kept for life.

I think I might haggle my SA tomorrow on the phone. I'll ask him if there's been a DTB on it or not.

Maybe the fuel line is clogged or getting pinched?

 

Chris,
Your injectors are connected to one another by a ringmain (pipe). You have a rotary pump that pumps filtered fuel from the fuel tank to the injectors. It maintains a specific pressure in this ringmain for the injectors to draw fuel from. Used to be 28 psi on Bosch systems - not sure on our cars.

This pump makes a high frequency buzzing whine which changes in frequency dependent on fuel demand.

If you have parked your car overnight & the pressure in the ringmain has dropped. If you stick you head out of the car when you first turn the ignition on prior to cranking you will hear the pump start & stop with some solenoid switching as it brings the system up to pressure & then stops. Same when you shut down. - the pump runs on to ensure pressure at the injectors should you wish to restart immediately.

This pump whine is absolutely normal.

 

FWIW, Have someone else drive and you sit in the passengers seat. Often where a sound comes from changes as you move around the interior. I think it is a good idea to jam your SA a little. Those guys can be preety good with excuses. Contrary to an earlier post, it is NOT your SA job to diagnose a problem-that is the tech's job. However it is critical to give him as much info as possible.

 

If the buzzing noise is loud enough to hear clearly it could indicate that the pump is either going out or a blockage before the pump is causing it to cavitate. In either case a fuel pressure test should show something.

While GM pickups normally have a loud fuel pump, I don't think I've ever heard anything from my w203 pump.

 

Not so! Bosch pumps have been singing along merrily for years. You have to listen for it but it's there. You won't hear it with the engine running unless outside the car. It would throw a code if line pressure was down. C55 NVH characteristics might mask it & it's likely a different pump. We are talking C240. The trouble is one gets sensitised to these things & they seem worse than they are.

 

Hey, nothing wrong with being sensitive about your car

 

True enough, but if it's something that is easy to hear as what you describe then something is amiss. I've had Bosch fuel injected cars since 1978 and they've all been quiet enough that I had to work at it, like bending over and sticking my head in the wheel well, to hear if the pump was working.

If it's a pump it'll make the noise all the time whether you're moving or not. From your original description it sounded like you only hear the noise when you're moving. That would exclude the pump from the list, as it's running all the time the engine is running.

Evaporative emission systems, which include the carbon canister, can make noises from time to time. For example, my wife's Audi TT makes a popping noise as the OBD II goes through it's checks on startup. It's remotely conceivable that the same pressurization (I assume that that's what it's doing) could be leaking through a loose hose. But then again, the leak would also throw a trouble code and light up the CEL so who knows.

 

All points mentioned are true.

What I can't figure out is why this sound would continue to get louder and more frequent.

My SA has heard it, but the tech didn't.

As was said before, the tech has to notice it. I need another ride-along.

 

+1 - Chris - you say and I quote "I hear the noise when I'm not even moving as well."

Can you have a better bash at describing the noise and when it occurs - also it's comparative volume to ambient noise - can you hear it when travelling at 40mph on a road with a good surface & the radio off?

Also - Your SM suggests that it's a common complaint. We had >200 of these vehicles in our company fleet and not one complaint about what the SM describes. (w203s not all 240s) Can you ask him what they do to rectify it? He can't suggest that all cars do it because it's patently nonsense if it's as bad as you say. I'm as sensitive as hell about noises - especially ones I can't explain. I'm very sensitive to the fuel pump noise but I know what it is. I'm equally sensitive to the line transformer high frequencies generated by CRT TV sets. Maybe that's why I'm more aware of Bosch fuel pumps.

 

Glyn,

Last night I took a drive just for you. I love my car.

Anyways, I drove around with the radio off, and then pulled up in my driveway with the windows down so I could listen.

I would describe the sound as a high-pitched "whisp" - not a squeek.

When I turned the car off, I could hear the sound for another 2-3 seconds, and then it stopped.

I could hear the sound at speed, even on the freeway at 70mph, though not as much because of the higher road noise.

I went to a close dealer today and talked with the parts manager as I was looking at some 2007 C wheels that I want to buy. He pulled up the part diagrams for that part of the car, including the fuel pump and the charcoal canister. He said he had never heard of it either. He wondered if the fuel pump might be suspect as well.

Just like others here, he said that if there was a pressure problem it would throw a code. Since none has been thrown yet...he was wondering if things were developing into one that would.