It could be because of chronic ie long term irritation .
He needs to take care of two things
1. nasal allergies / disease like blockage,discharge etc if you have,,,, as the nasal discharge fall back in throat and irritates it.
you need to consult your ENT specialist
to get examination and CT scan
nose with plain coronal views limited cuts,, if required to rule out any disease in nose and paranasal sinuses
2. Take care of reflux, It is one of the reason for recurrent throat irritation
,, it doesnot matter you feel heart burn acidity or not.
Take--- Antacids and antireflux medicines .
Keep head end of bed elevated.
Avoid alcohol, Smoking
Do brisk walking daily
Go for walk after dinner
Avoid spicy food
Avoid late night coffee