Hi there. I'm very sorry to hear about this issue. My name is Linda and I am a vet with 10 years of clinical experience; hopefully I can help you today!
Excessive vocalisation like this can have a few causes including:
- An overactive thyroid
- Feline dementia
- A source of pain such as arthritis
- Reduced vision, sometimes caused by high blood pressure
I agree with your vet that a check up is a sensible step and I'd want to know whis thyroid levels have been checked and he's had a joint exam / mobility check.
This should not be particularly costly.
If health issues are ruled out, we'd start to consider feline dementia more strongly.
As well as being vocal, we may also see signs such as altered behaviour patterns, socialising less, staring into space, being restless, struggling to sleep etc.
While we cannot cure dementia, it may help to start brain supportive supplements, to keep routines the same and to encourage 'brain games' during the day. Brain games are things like food puzzles and interactive toys.
I hope we can get some answers soon as I know this must be a worry for you.