Hi, I've had a metal rattling sound underneath my car coming from the rear. One of the coil springs had broken, so I had those replaced and I also had the rear shocks replaced, but I still hear the sound. I hear it when I go over even the slightest bump in the road, but it's especially bad when going over speed bumps or if I hit a pothole. Someone said it might be the heat shield and another person said it might be the rear sway bar. Anyone else have this problem? It's a 2008 Mazda 3.

 

Is the rattle a light or heavy sound? If it's light (tin can), there is a good amount of metal heat shield under there, and snow and such does bend it on occasion. It should be easy enough to crawl under there and tap on different pieces to see what is loose. Most of it is easily reachable and you can bend it back into position.
The sway bars and such can be jiggled if it's on level ground and see if you can reproduce any looseness.