Sound lagging in the game.

When I first played this game, the very first time everything worked perfectly but recently playing it again I found that cars don't make any noise when you are driving till a few seconds later then you hear the engine noises, same for car horns.

Is this an issue others have had with this game and why is it?

I find I have to keep one or two other programs open to tie up my CPU then the game plays properly.