The causes of the tapping sound in the ear with the mouth open may include excess cerumen, temporomandibular joint disorder syndrome, and abnormal opening of the eustachian tube. 1. Excessive cerumen: Due to excessive cerumen in the ear, when the mouth is opened and closed, the movement of the cartilage drives the cerumen to touch the tympanic membrane, which will cause a tinkling sound. 2. Temporomandibular Joint Disorder Syndrome (TMJDS): When the mouth is opened, the gap at the back wall of the temporomandibular joint capsule compresses, causing friction sounds when the temporomandibular joint moves, resulting in the ear moaning sound when the mouth is opened. 3. Abnormal opening of the Eustachian tube: the Eustachian tube mucosa atrophy, muscle coordination dysfunction and other mechanisms cause Eustachian tube dysfunction, when the mouth is open, the Eustachian tube may open excessively and produce a murmur within the tympanic cavity, which is manifested as a zipping sound. If the symptom of the ear noise when opening the mouth continues to be unrelieved or occurs frequently, it is advisable to consult a doctor for a definitive diagnosis.