My father (76) has gradually started to sort of sound differently. He sounds as if his tung
Is heavy . He does have a deviated septum and a polyp in his nose. He doesn't drink at all so its not from drinking (although it sounds like he is) also he has no other stroke like symptoms and is in otherwise perfect health. Any ideas of what this could be?

It could be he is having motor skill problems
Anxiety,
He could be getting less oxygen to his brain and possibly plaque build up, which COULD lead to a stroke.
It could be a number of things but more probably related to either brain, nerves and/or muscular problems.

He needs to get to the doctor and see exactly what is causing it.