The easiest thing to do is free up about 40 free hours. Take off all 4 door panels, the headliner, the seats, glove box...pull back as much carpet as you can, remove the plastic around the A B & C pillars, and take out all the trunk trim. Get a crap-ton of sound dampening material (Dynamatt if you're rich, Raammat if you're not) and go to town. Don't forget to caulk the trim piece along the base of the front windshield (stupid rattling clips)
You should be rattle free after that!
...check the swivel seat belt connections, I had a squeek coming from there once.