Several drugs cause hearing loss. Blood Pressue meds are one, Vicodent (pain med) was posted as another.
Also the medical community often miss things like pinched nerves due to cervical disc degeneration in the neck. (mine make my arms go numb and burning pain in my left eye socket, and have also caused occassional numbness in my right ear with some temporary reduction in hearing in that ear).
The meds he takes need to be really checked into for side effects. (ever try to read that #6 pica print on those insert for meds?)
Noise is also an unlikely cause of his hearing loss, because noise-induced hearing loss occurs gradually over decades, not months. Of course, if a hand grenade goes off in your immediate surroundings the onset of the loss might be a little more sudden....
Because it doesn't sound like his hearing loss is responding to therapy (mind you, I'm going by his statement and have no access to his medical records), it could also be a genetic hearing loss. Cochlear implant surgery is extremely successful but we generally hold off until we are quite convinced that we can't preserve whatever residual hearing a patient still has. People with cochlear implants are quite capable of holding a conversation over the phone, so there's still hope for "Open Line Friday"