Under ideal conditions, these tubes open briefly when you swallow, yawn, or chew. But when the pressure outside changes rapidly (in an airplane or scuba dive) or the tube lining becomes inflamed from allergies, sinus infections, or the common cold, the tube gets stuck shut. The air inside your middle ear gets absorbed, creating a vacuum that pulls the eardrum inward. That “blocked” feeling? That’s your eardrum being stretched painfully. Popping it—forcing the tube open for a split second—is simply the sound of pressure equalizing.