The eustachian tubes connect the middle ears to the back of the nose and help the ears drain fluid. They also help to keep air pressure between the outside air and the pressure in your middle ear equal. When there’s a sudden shift in air pressure, your body adjusts by moving air through your Eustachian tube and thus the "popping" sensation. This change in pressure can occur in exercisers when breathing forcefully or bracing to lift a heavy load and thus causing the "popping" sensation. Swallowing or yawning can help unplug your ears.