A couple days back, I noticed a (seemingly) new sound - a metallic-sounding rattle coming from the back of the car under acceleration. I was able to replicate it yesterday in a video. My first move was to check the exhaust to see if anything was loose. Nothing's jumping out at me, but maybe there's a heat shield I missed? I need to get under the car and take a more in-depth look when things dry up a bit outside. Anyone have any thoughts about what this sound could be?