Almost everyone's familiar with the ear pop that accompanies take-offs and landings in planes. For the most part, they're pretty harmless and are usually preceded by some savoury candies, so I'm not complaining. If you have a cold while this is happening however, then say a prayer and stuff a hundred Alpenliebes in your mouth, because you're in for a world of pain! As to the reason why this pop happens in the first place, audiologist and clinical associate professor from NYU Langone, William H. Shapiro puts it pretty succinctly.

When the pressure does finally get equalised, you can feel it inside and consequently hear that signature pop!

To equalize the pressure between your inner ear and the atmosphere, the air from your inner ear needs to escape through the Eustachian tube. When a flight ascends or descends rapidly, this Eustachian tube doesn't get enough time to balance the pressure immediately. This can take even longer if you have a cold and congestion.