LOL, I love when threads start like this!
Seriously though, I had something like this happen. Put your car back up and look above your drive shaft where your emergency brake line splits. I had this happen to my ride and it was freaking me out. It only made the noise when I was hard on the gas and the clunking happened at a higher frequency the faster I was going. The splitter bracket, that holds my E-brake cable, had detached from the frame and fallen down far enough that it was rubbing on my u-joint. I just fastened it back into place and problem solved.
Take a look underneath, you should be able to see rubbing marks on your drive shaft. Mine is an S14, not sure if its the same for S13 or not.