Take a good look at him and see if his ears move. If they are not cupping at sounds, he may have gone deaf and is trying to compensate.
One of ours lost his hearing about 5 years ago and the constant talking was an indication of it, he could feel his meows, but not hear us and was overcompensating trying to get attention. We gave him more physical interaction, which helped him adjust to a silent world. Since he coulnd't hear us anymore we started using hand signals with him as well.