Why do older or high mileage engines sound so much better?

[dinkel]

My trusty 1.3 now has 241K kms on the clock and with a new cat and exhaust (2 parts) fitted it still has that droning hum - and pops 'n bangs in the lower rev register - I thought was due to the slowly dying exhaust.

It's the same darkish quality - I like it - those old racers have, when I enjoy them in the paddocks of various classic car racing events.

Is it play between the parts, or what?