So, for the past few months I was noticing at certain frequencies that the rear dashboard emanated a rattling noise that was quite noticeable. It got to the point that I fixed it. There is small wiring in a hard plastic tube near the third brake light and sub that rattles at certain frequencies. Adding sound dampening foam and/or taping it down worked for me. No more sub rattles.

Here is a link to a video of a guy having similar troubles who fixed his similarly to mine.

https://www.youtube.com/watch?v=vsSICacg-Uc