one word to fix that drone (or eliminate most of it) - dynamat!!
The stuff is awesome - it is a sound insulating material that you stick all over the interior metal of your car - I lined my trunk and especially the metal under the back seat (that is where the bulk of the noise seeps in) - made a HUGE difference. The drone is still there now and then, but not nearly as head splitting, and over all it is a big improvement.
The stuff ain't cheap though - about $250 to line the trunk and under the back seat, but well worth it in my opinion. You can find the stuff at Best Buy and most good audio shops - just wear gloves when you work with it as it has a thin metal backing and will slice you up something nice.
Hope it helps.