Borla S Type exhaust had a recall on their resonators. After getting the new one in, I started hearing rattling around 1500 rpm.
When getting the ST up on ramps, I noticed a screw was a fraction of an inch away from the top of the mufflers. They only made a noise when I slightly lifted the muffler upward. I put a piece of plastic between the screw and the mufflers. No more noise.
I wanted to share this in case anyone ran into the same problem. Pictures included.