Timelapse of steel near to the payload door being warped slightly during peak re-entry heating. This is in the area where tiles were removed

Listening to this Booster 13 Igniter test on max volume, you can actually hear the difference between the number of engines in each group of the ignition sequence.

1st pulse: 13 Center engines
2nd pulse: 15 Boost engines
3rd pulse: 5 Boost engines