Here's my update so far.
- I checked, then loosened and re-tightened the caliper bolts on all four corners. I could not find a loose bolt.
- I have not yet checked for brake pad material that has separated from the brake pad backing plate.
- I found play in the driver front caliper, enough just to rock it a little, and noticeably different from the passenger front. When I took the floating half off, I found a little play in the integral sleeve. I took a video below.
https://www.youtube.com/watch?v=oTRUk--PLJA
I have a hard time thinking this is the source of it somehow, didn't seem like enough play. Anyone have experience with it?