Play a good, bass-heavy song, go to your lid and see if you can place your hand on an area and get it quiet down or stop all together. If you can do this, get some Dynamat from your local audio shop and place some on that area. You may have to remove some panels, as this stuff needs to be applied to a metal surface.
Hope that helps....
-There are 10 kinds of people. Those who understand binary, and those who do not.
-If we ever forget that we are One Nation Under God, then we will be a nation gone under...Ronald Reagan