Exhaust drone is a tricky problem. Unlike the sound that comes from the tailpipe or intake, exhaust drone isn't directly a result of engine noise. It's a sympathetic vibration that develops in the exhaust pipes resulting from often-inaudible sound waves emitted by expanding combustion gases. These pressure waves travel through the exhaust stream, bouncing off the walls of the exhaust tubing and causing it to act like a speaker. Unfortunately, reducing or eliminating exhaust drone isn't quite as simple as swapping mufflers.
Instructions
1. Unbolt the tubes running from the catalytic converter to the tail-pipe, known as the cat-back section, and remove them. Replace the tubes with a larger diameter, thicker-wall set of tubes or cat-back system. This goes right to the core of the problem, since thicker tubes have a far lower resonant frequency than thin tubes. Replacing thin-wall steel or titanium tubes with thicker-wall steel tubes will add some weight, but it may also solve the problem altogether. Installation procedures will vary greatly by vehicle, so follow your exhaust manufacturer's recommendations.
2. Wrap the exhaust pipe spanning from the exhaust manifold/turbo to the catalytic converter with a layer of heat-insulating header wrap. Wrap the tube with a double-layer at the manifold/turbo flange and secure it with an exhaust clamp. Wrap the tube in spirals so that each spiral overlaps the last by 1/2 inch, and secure it on the converter end with another exhaust clamp. You could replace this section of pipe with a thicker-wall tube, but there's a lot more effort and cost involved than just wrapping the pipe.
3. Cut a section out of your cat-back exhaust system about 12 inches away from the converter and install a resonator. You've got a couple of options here. You could use a junkyard resonator from a vehicle with an engine of similar displacement and engine type, or you could install a 6-inch cherry bomb-type muffler in the pipe. The cherry bomb won't target high-frequency waves as accurately as the stock resonator, but you can find a cherry bomb to fit almost any sized exhaust pipe, and it's small enough to fit almost any application.
Tips Warnings
If you go with the cherry bomb option, you might want to use a pair of 6-inch cherry bombs spaced about a foot apart. A single 6-inch cherry bomb is just the right length to catch most of the high-frequency waves, but it doesn't have enough packing or room in its expansion chamber to effectively catch all of them. The second cherry bomb will scavenge most of what your first one misses without killing your engine's low-frequency growl.
