After taking out the entire back seat and lining, and the entire trunk EVERYTHING, I realized that I could not access the fuel tank from the cabin or trunk! Oh what a night...!
I took some photos and I might as well post them anyway. This is of the back end of the trunk with all peices and linings (except for trunk side lining) removed.
This next picture is where the back seat backing goes. The pic was taken from the passenger side rear door.
I got no where tonight... I hope that my mechanic can check it out tomorrow. I am sure if he puts it up on the lift, he'll be able to see what's up.
And just to add to my original post, I hear a very loud sloshing and thunks as the tank is hitting something.
((And just for curiousity, what is this? It is under the rear seat in the center. I would think it's the parking brake cable... can you adjust it here? And if so, do I need to? (Or was it only adjusted once at 15k miles?) Thanks!))

(left side is rear of car, right side is towards the front)