I sounds like a short beep or "zip", right?
I'm quite sure that this is a side effect of the auto-fading feature of the hardware codec (GAIN_STEP in register AUDIOSET2). Last time when I tried to disable it, there was a click instead of a zip when stopping playback.
Ideally, there should be no click nor a zip, of course. We might want to try disabling this auto-fading feature again.