Exhaust! :shrug:

Yeah you can put a new x-pipe or h-pipe on it will sound a lot better. However the overall tone of your car comes from the mufflers, so I would probably change your mufflers first. check out www.mustangexhaust.com if you have no clue as to what cat-back you want.

Stock mufflers with an X pipe or H pipe would be deeper, but not as loud as if you added aftermarket mufflers.

The cheapest way to "get loud" is to have a shop weld in some mufflers. You could have this done for about 250 bucks (that seems to be about what most people pay), which includes the cost of the mufflers. For about 100 bucks more, you could get a whole catback system.

A good resource to check out is www.mustangexhaust.com

They have lots of sound clips on just about any combination.