If it's the bead-type cat, it will have a very flat bottom with a plug near one end. You can undo the plug & some little black beads about 1/8" in diameter will fall out. Many more will fall out if you race the engine or drive around the block a few times. More noise will also come out, but that's probably OK for a short time. The beads may stain the driveway, so be forewarned. Replace the plug (I used a freeze plug, 1-5/8" I think, but you better check for sure).