A 35-year-old man presents with a 3-month history of aural fullness and mild conductive hearing loss (15 dB). Otoscopy reveals a retracted tympanic membrane with prominence of the malleus handle. Tympanometry is performed and shows a peak shifted to negative pressure at -250 daPa, as marked **A** in the diagram. Which of the following is the most likely pathophysiologic mechanism underlying this tympanographic finding?