What happens to the human ear as it naturally goes deaf? I was always told that when the human ear goes deaf to a specific sound (auditory frequency), then that sound is heard one last time, and upon fading away, will never be able to be heard again. Is this in fact true? If so, why do we hear that sound (which seems to happen randomly and is somewhat loud for a split second) just before the ear becomes deaf to it? Ultimately speaking, what exactly happens as the human ear _naturally_ goes deaf?

I don't think you will hear the frequency "one last time", before it fades away. More likely you will slowly lose your range of hearing from high to low frequency.

Hair cells in the cochlea are arranged in a spiral on the basilar membrane, with high frequency cells at the apex. For some reason, high frequency cells are more sensitive to damage, either by loud noises, drugs (including certain antibiotics that cause deafness), or old age. By adulthood, humans have already lost a significant portion of their high-frequency hearing (children hear up to 22kHz, adults 16-18kHz from memory).

Significant hearing loss can also be caused by the loss of outer hair cells, which act as a cochlea amplifier, or loss of the type I spiral ganglion neurons that connect the hair cells to the brain. But typically age-related hearing loss is normally caused by the death of Inner Hair Cells.