I can't hear it over the engine.
If yours is really bad, you might put some stick-em sound deadener between your tank and the car body. It may be using your unibody as a speaker cone.
Nothing an x-pipe and some free-flowing mufflers won't address. Keeping the tank full can help too. You can add the sound-deadener mentioned, under the carpet in the trunk area works too if you're hearing the noise inside the car. If you're hearing it with the windows down, none of that will help really. I got used to it and actually started to like the sound - as it's the sound of more horsepower potential - so maybe give it some time.