He might be deaf

Siamese and Bengal's are a talkative bunch

My dear Zoe was like that, she talked all the time whenever people
were around, and did it for most of her life.  She was a tortie and a
total clown and loved any sort of attention.  I used to have meowing
"conversations" with her.  I think she felt it was her job to always
let me know where she was, just in case I felt the need to play with
her!

I've heard of a few cats that like to talk

Cinnamin

I don't think it's breed related.  My two cars are both black American
Shorthairs also, and they are opposite as day and night.  Yoda is
quite, sweet, and passive while Onyx is hyper, playful and --as with
your cat -- is very vocal.  SOmetimes I get really annoyed because
he'll "talk" to me constantly and  have no idea what he wants.  
Clean litterbox.  Check.  
Plenty of food.  Check.  
Plenty of water.  Check.  
His toys aren't stuck under the furniture.  Check.
Yet, meaow, meaow, meaow. I'll pet him, scratch behind his ears, he'll
purr loudly for a minute, go chase his mousies around for a few
minutes, get bored and five minute later he's meaowing again. He's
very healthy and happy; it's just what he does.   He's a crybaby.

Oh, and Onyx also "chatters" at birds and squirrels through the
window.  It really is funny. It's not quite a growl and not quite a
meow.  I have a ground-level feeder that attracts mourning doves and
cardinals as well as the squirrels, and it is right outside a sliding
glass door in my living room.  The critters have gotten to know that
Onyx cannot get the through the glass so they ignore him.  Sometimes
they will be 2 feet from him happily eating their sunflower seeds
while he "chatters" away at them from the inside.  I wish I could
describe the sound that he makes; it really does sound like he's
"talking" to them!  It's a hoot!

---
Zob