It appears that, instead of having a separate, properly defined sound event, wardens instead recycle an existing sound event for this specific case.
To reproduce:
spawn a warden in an isolated pond with absolutely no distractions
/tick sprint 55s
wait for it to despawn
note the captions
Results: “Warden groans angrily”, as though it were tracking a mob or other vibration source
Expected: a more fitting caption
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