whats happened to his voice?

I watched an interview with him on the Colbert Report like a month ago, he sounded very much the same, I think any difference is the fifteen years between the Big Lebowski and now, he was 49 then and is 64 now. So I assume it is just age.

Its put on.. He sounds same in few films, wild bill.

He is acting..... Its put on.

It's acting! Part of the charecter.