|MadSci Network: Anatomy|
I agree with the previous answer that it is most likely that you are hearing sounds conducted from other parts of your body. If you are clenching your jaw you may be hearing movements in your temporomandibular joint. One other very unlikely possibility is that you are able to voluntarily contract your tensor tympani or stapedius muscles. These are muscles attached to bones in your middle ear which dampen sound being transmitted to your inner ear. It should be possible to record changes caused by these twitches using a device called an impedance audiometer which many audiologists and some pediatricians have.
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