Suspension Still Rattling Over Rough Roads - Replaced Trailing Arms Already
 

Any clues? Anyone have this issue too?

I would start by inspecting all bushings and ball links and also the top of the struts. The drop links can also rattle if they are worn.

Once you have dealt with the most common failure points you have to start checking everything else. The good news is that it is a lot easier to identify a failing component.

The stabilizer/sway bar bushings are a cheap easy job and are probably due for replacement even if it's not the cause.

Neil made some great DIY videos while he had the Boxster:
<iframe width="560" height="315" src="https://www.youtube.com/embed/IEVIZmUDgug" frameborder="0" allow="accelerometer; autoplay; encrypted-media; gyroscope; picture-in-picture" allowfullscreen></iframe>

You might want to check out the rest of his Channel for more Boxster videos. https://www.youtube.com/playlist?list=PLNKrPMJBU7Wju1zDzxagvESn0QN2JDdkF

How many miles on your car? If it's over 80K or so, you are looking at a long list of things to replace.

As far as the rattling goes, I'd look at the drop links first. And by look at them, I mean replace them. While you are it, go ahead and replace the sway bar bushings as well. Those are the easiest things to replace; once you've done that, then you are looking at big items like shocks, strut bushings, LCAs, etc.

When I got my high-mile (148K) '02, the suspension made so much noise rattling, knocking, and squeaking that I ended up just replacing everything in the suspension except the rear toe-links. It was a real project, but it transformed the car.

63200 miles on car. Thanks for the tips, all! I'll check them out.

Really thing about replacing drop links. OEM DL's are only about $25 each and easy DYI.
Had a 98 Boxster years ago that I bought to repair and sell that sounded so bad I thought I had a bad strut mount (or strut).
Drop links solved the problem.