Common trunk rattles?

[johnjj728]

I am currently running a Resonant Engineering 18XXX and a Directed1100d in my car. The sub box is about 9.5 cubes tuned to 30hz. I have deadened my trunk lid and it hardly rattles but the underside of my car will not stop rattling. Sounds like maybe gas tank or something else under there. If anybody knows some common undercarriage rattles let me know so i can take care of em. Thanks, John