Jim Stratton

My new (to me) W211 with 107k miles has had a rattle from the right front since purchase. I use a local, very experienced MB mechanic recommended to me by someone I trust and he has thus far replaced the thrust arm and lower control arm with no change in sound. He did so because he heard and felt a knock on the thrust arm when his helper (slowly!) drove up and down the driveway lip at his shop.

The high frequency (in terms of speed, not sound) rattle occurs regardless of ambient temperature (I'm in south Louisiana and have had temps from the 30's to 80's since purchase) or speed and seems to correlate with pavement roughness...smoother pavement means fewer rattles. I changed the cabin air filter and noticed that there were 2 hose lines with thick rubber grommets that sit atop the windshield wash fluid reservoir that when I bounce them on the nearly-empty reservoir made a similar sound to what I'd been hearing. I then filled the reservoir and the sound pitch changed when I manually bounced the lines on the reservoir, but the sound when driving remained the same so I ruled that simple fix out. The rattle sounds like an undamped shock but the car doesn't bounce when manually pushing down, or if you took an empty plastic reservoir and put a couple of rocks inside then shook it but I don't think there are rocks inside the wash fluid reservoir. The mechanic told me that he has only seen one forward strut go bad on the W211's and that my upper mounting bolts are tight and the suspension was all tight when he had it up on the lift, but that is our next part we're thinking of changing (he hasn't charged me for the parts he put on that didn't fix the issue...not too many of those guys around anymore). The sound can only be replicated when driving with the suspension under load and not on a lift or jack stand. If anyone has had a similar issue that they resolved I'd sure appreciate your solution.

Zach8131

Hey Jim,

Welcome to the forums and hopefully we can help you find the rattling noise. Most posts will be a shot in the dark since we cant physically see the car, and will just provide our 2 cents with our experience in these cars.

I assume based on your description that you have conventional struts/springs as opposed to airmatic suspension. Is that correct?

If there is a rattle I would first start to check the wheel bearings. I had a similar issue with the driver's side and the rattle went away with the wheel bearing. They were original to the car (I did them in December and my car is a 2008 E350 with 187,+++ miles). Over time they get loose or worn down and cause play. Hopefully they have not started to fail internally causing the bearing pellets to make that noise. In any case, you can take your tire off and pop off the cap of the wheel bearing to have a look-see. If you do need to replace them, I heavily recommend doing both at the same time, and buying the whole assembly rather than just the individual bearing to press into your existing hub assembly. Also purchase new locking nuts. They do go bad after heavy use, Some people say the nuts don't go bad, but I always go with the side of caution for such a vital part of the car.

Another issue may be dry brake guide pins or very cheap brake pads that rattle around in there. I have had that happen a long time ago on a different vehicle (05 e320)

Hopefully this helps!

Jim Stratton

Zach,

You are correct, no airmatic. The mechanic checked the bearing play by checking the wheel wobble with the wheel on the car and I just did the same and the hubs don't feel loose, only minor play up and down and laterally. We just replaced the bearings on my wife's Acura MDX because I heard the standard "whomp, whomp, whomp" sound at speed and that's not what I'm hearing either. Those are good thoughts about the brake guide pins and/or brake pads and I'll ask the mechanic to take a look when I take it back to him next week. I'd characterize the sound as much more 'plasticy' sounding, like what I described in the first post, rather than metallic and it is not a thump like you'd expect to hear from bad ball joints. I'm not saying its not those, but the mechanic drove the car and he and I are hearing the same thing. Its VERY easy to hear the sound unless I turn the radio up like I'm reliving the 80's so its quite frustrating to not have a solution even after changing 2 components.

I appreciate your quick reply and good thoughts, we'll take a look at your ideas.

ot1

try jacking up car, get underneath with heavy rubber mallet and beat on suspension components or various other parts to isolate noise.

could be the stab bar links knocking, upper 12mm socket head bolt loose.