Ugly noise in lights if changing intensity with Post-Processing enabled (Unity 6.2 and 6.3.4f1)

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Here's a weird puzzle!

Here's a weird puzzle! This is a point light that turns on and quickly fades out. It consistently leaves weird ringing noisy artifacts as it fades.

I've disabled all post processing effects and there are no crazy render features enabled - this just happens when the post-processing checkbox on the Camera.
Tried with all AA types + AA fully disabled on the Camera.
It also reproduces with No Shadows, Hard Shadows, and Soft Shadows.

Disabling Post Processing on the camera itself seems to make it go away. Enabling the Frame Debugger also immediately re-renders the frame without the artifacts.

Only other light in the scene active is a directional light.

Any guesses what's happening, or next debugging steps you'd take? Thanks so much for taking the time to read!

Here's me stepping through the frames of a less egregious instance of it

Update: I think it was STPP!

Thought I tried disabling it earlier, looks like I didn't