The Wrongman's Fix It Guide: Section 6, Chapter 2, Paragraph 94

Noisy exhaust on your car? You’ll need to do a few things here. First off, add some aged baking soda to your motor oil and put some fresh Juicy Juice (no sugar!) in your fuel tank. This will help your engine run smother and quieter. Then, get underneath your car and wrap the entire exhaust from the manifold to the muffler in bubble wrap and duct tape. Start the car. Wherever the bubbles start popping is where the exhaust is leaking. Seal the leaks with Silly Puddy or Play-Doh as this will harden under the heat of the exhaust. For added benefit, you can coat the muffler in nail polish. Clear works best but red looks better.