For example, when you hold your nose closed and try to blow air out of your nose.
In: Biology
It opens up the eustachian tube which connects the middle ear and the larynx. This allows the pressure behind your eardrums to equalise with the environmental pressure, which makes transmission of sound clearer.
Essentially there’s a change in external pressures which causes some discomfort in your ear when it doesn’t naturally equalize. So when you yawn or whatever method you use to equalize the pressure the “pop” is the pressure equalizing suddenly.