A 35-year-old woman from Tamil Nadu presents with a 3-year history of painless, progressive hearing loss and recurrent ear discharge from the right ear since childhood. She reports occasional vertigo triggered by loud sounds (Tullio phenomenon). On otoscopy, a white, pearly mass is visible in the posterosuperior external auditory canal. Tragal pressure causes vertigo and nystagmus. Weber test shows conductive hearing loss on the right. What is the most likely diagnosis and what is the underlying mechanism of the Tullio phenomenon?