The noise cancelling headphones are listening to noise coming from the outside and cancels them out. When the source of the sound is in your mouth (see also: bone conduction), the headphones can’t hear or cancel that sound.

The headphones should still cancel the background noise as usual, but they can’t cancel whatever noise is coming from your mouth. I wonder if this mismatch could result in some noise getting through?

If you’re wearing buds, the seal could become inadequate while your jaw is moving, so that could also explain some of the noise.

A static type sound can occur while biting where you eustachian tubes are cleared. The same thing can happen when yawning (it is why yawning is encouraged when feeling inner ear stress while taking off in an airplane).

It happens without earbuds too, but might be more noticable.

I can personally pop those voluntarily, as I'm a scuba diver, and you have to clear your ears quite frequently.

Think of noise as a sine wave on a Cartesian plane (the X-y graph you used in math class). The noise goes up and down so that y=1 at the max and y=-1 at the minimum.

What happens if we add 1 when y=-1? Well, now it’s 0. And what happens if we add -1 when y=1? It’s 0 again. That’s basically what noise cancelling does. It adds the “opposite” to make the sound equal 0. That’s super layman’s terms, but I hope it makes sense. It’s basically trying to make the opposite of whatever it hears.

But when something is physically touching your body, your ears can’t absorb that “opposite” sound because the original sound is kind of already absorbed in your body, if that makes sense?

noise cancellation should be better at adjusting for sounds which occur for longer periods of time. it takes time to calculate the inversion, the amplitude, the frequency, the emission and line them up.

What does popcorn sound like?

Don't know.....but maybe don't bite your nails. Just in general.