Welcome, mposler
Heat shield rattle has been an issue with Subaru for decades. I've owned six Subarus and they all rattled at some point. If you search "heat shield" on this forum you should find numerous threads dealing with it. Short answer is someone needs to get under the car, find which one(s) is/are rattling and secure them by re-welding, using large hose clamps, or a few other creative fixes forum members may have used.
Good luck.