After working on the radio I decided to see the state of the stock sub. Removing the seat and sub showed the speaker to be in pretty bad shape!
It wasn’t moving at all when playing music and when I measured continuity across the contacts it measured open, bad speaker. I should have a replacement on the way and hope to get it all back in working order. 🙂
My speaker (12-264TAP) showed up 2 days early, install was a breeze, and it sounds pretty good.