You can install "Glass Packs", or "Cherry Bombs".
These are mufflers with a special device inside that reverberates the noise between sandwiches of laminated glass. The glass is sized and spaced precisely to cause a nicely tuned sound.
Alternatively, you can install customized exhaust, like Borla or Flowmaster.
These will not necessarily make your car sound louder, but it will take your factory sound, and run it through a tuned pipe that will give it a beautiful melodic sound.
The "noise" other people are complaining about does not come from after-market exhaust pipes, it comes from a car with NO muffler. Sometimes, in an effort to improve performance, people remove mufflers from their car, so there is no back-pressure. The theory is the engine will breathe more freely. This is illegal in most US states, and the performance increase is negligible. It also tends to pollute the air if they also remove the catalytic converter when they remove the muffler.
The method of choice is to purchase after-market exhaust pipes, leave the catalytic converter installed, and tune the sound. You can listen to samples on YouTube, or visit a local car show and ask the owners what kind of exhaust they have installed.
