There's a scraping sound on my rear suspension for my 300SD as I move over any sort of bump. It gets really disconcerting since I hear it all the time and am nervous there's something seriously wrong with the rear suspension. It's definitely a scraping like noise and not a thud or a creak or anything else.

I don't think it's the springs since that sounds more like a creaking noise anyway.

I've been thinking it's the shocks, but I don't know how I can otherwise tell. Is there a tell-tale sign or way to check their quality? Even if I have to remove it.... How might I check to see it's life?

Someone suggested it may be the sway bars. I'm not sure what exactly the purpose of the sway bars are. Can someone elaborate?

How might I be able to tell whether the sway bars are problematic? What can possibly go wrong with them? Should I be able to re-create the scraping sound somehow, perhaps by disconnecting the bars from the link and moving each piece in full to see if I hear/see anything odd? It would especially be nice to try and pinpoint it without having to remove the shock and/or spring. And I'd like to avoid paying for replacing things I don't know the quality of, especially when we could be talking hundreds of dollars.

Then there are bushings.... I've been told the trailing arm has bushings - where are they? The little rubber stoppers that the trailing arms hit up against on the body seem to be in decent shape. The rear differential mount seems okay too.

Any other possibilities? I've had the car 6 months and haven't done anything to the rear suspension and the noise hasn't gotten much different, but I'm trying to ascertain the severity of the problem and worth of fixing it in the 25 deg F weather. I'd like to be able to pinpoint the issue in my garage without constantly driving the car and tinkering, replacing, etc.