Can't tell exactly where the rattling is coming from but it's definitely on the passenger side near the rear wheel.

81 300sd

I've been driving it for the past couple weeks and everything has been fine, but today is the first day I've taken it for an extended long drive. Only after going 80 mph for 30 min to an hour do I hear this rattling noise reoccuring. If I pull off the freeway and stop, and then get back on and get back to speed the rattling goes away for another 30 to hour. It originally started after about 3 hours of continuous driving. The road is relatively smooth, no potholes and we didn't drive over anything that would have messed up the drivetrain or suspension. Any ideas what it could be? I've made a video of it and will post it when we get a wifi signal.

I would lay considerable odds that these are worn: http://catalog.peachparts.com/ShopByVehicle.epc?q=1984-Mercedes--Benz-300sd-Suspension&yearid=1984%40%401984&makeid=63%40%40MERCEDES+BENZ%40%40X&modelid=6208%3AMBC%7C1510%3AED%7C10000134%40%40300SD&catid=241464%40%40Suspension&subcatid=241475@@Sway+Bar+Link&mode=PA

Very simple to replace.

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Sam

84 300SD 350K+ miles ( Blue Belle )

I would also think that though mine were rattling whenever I was backing down my driveway or clearing a curb... if so, these are very easy to replace...

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1987 Mercedes 300SDL; SOLD
1985 Mercedes 300D; SOLD
2006 Honda Pilot - wife's ride; 122K;
1995 Toyota Land Cruiser - 3X locked; 182K

I had a similar sounding noise for the past 3 months. I just took it to an Indie to have it checked out. Now it's fixed & I'm $365 lighter. It turned out to be rusted emergency brake cables just about grabbing the rear right brake shoes & one of the shoe springs was rattling periodically. I had all replaced. Now it's fixed.