How do you turn off "plink" sound from Mute button in 15.3.1?

I've had a couple weird default settings appear since installing iOS 15.3.1 on my iPhone 7. I'm working to solve the nastiest one -- random notification vibrations, seemingly not related to any app -- but another one I've just discovered is a pair of slightly varied, loud "plink" style sound effects triggered when I mute and unmute on a speaker phone call.

Does anyone know where to turn this off? (I'm not sure why anyone would think an audio cue is needed at a moment when the user is looking to silence things, especially since there's a brightly lit button that indicates the mute status, but...)