The message
from "R.P.McMurphy" contains these words:

Nice explanation! Must be the same reason why a milk frother is so noisy
too!

Certainly is.

What I can't find is the explanation for why the sound of tapping a
spoon on the bottom of a fresh poured drink rises in pitch as you
continue to tap. I saw one a while ago, but I can't remember the
details. Something about microbubbles changing the speed of sound in the
liquid but that doesn't always seem to fit what's happening.

--
Skipweasel
Pay no attention to that man behind the curtain.