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Eustachian Tube Dysfunction can be caused by large adenoids, allergies, or a cold. This dysfunction can cause crackling or popping noises in our ears. The tube is lined with moist mucosa, and inflamed Eustachian tubes often get sticky, which causes the crackling and popping noises when the tubes are moving around. If the inflammation is serious, it can be easily treated with steroid nasal sprays.
Just like you can have a spasm or twitch in your eye muscles -- or indeed any muscle -- these muscles cause a unique sound sensation in the ear when they repeatedly twitch with high frequency. The plugging/unplugging sensation is likely the Eustachian tube, which controls the pressure in the ear, opening and closing.