There are two means to quiet the exhaust systems found on most street bikes today: restrictive and absorption mufflers.
The stock muffler falls under the restrictive category. It uses a steel baffle design, which causes disruption of the sound waves by redirecting them through a series of plates, or baffles. These baffles are permanent, and unless corrosion is an issue, never really need replaced. They restrict the amount of air flowing out and disrupt the air flow pattern.
In contrast, most aftermarket pipes, which are notably louder in volume, are absorption-type systems. They do not have plates to redirect sound at all, so these are called "cores". They use consumable products like fiberglass or stainless "steel wool" to soak up the waves, sometimes in conjunction with a perforated core. Over time, the packing burns and disintegrates and the bike sounds progressively louder. To return to the original sound, the core must be repacked with some heat-tolerant material.
There are no true "baffles" on the Roadhouse Slip-Ons. If you hold the muffler to the light, you will notice the catalytic converter is gone, and you will be able to see straight through it. The standard core has perforations and indentations downward into the path of the outward airflow. The quiet core also has indentations, but these protrude even further into the hollow center of the muffler, causing additional airflow disruption. Not quite as much as a baffle, but enough to prevent the straight-through tunneling effect of a solid core (think in comparison to straight pipes, Cherry Bombs, etc).
So, how do we quiet the Roadhouse Slip-On? Two ways - either repack the standard core with more sound absorbing (yet flame-proof) material, or install the quiet core.
To remove the Slip-On's core, you will need to remove the slash tip and the retaining bolt. The tip is removed with two bolts, one on the underside and the other on the tire-side. The core's retaining bolt is just beside the tip underneath. Now for the fun part of removing the core itself. I found that a paint can opener (the type with a teardrop handle at one end and a little lip at the other) works well. Hook the lip onto the first perforation you can grab, and give a gentle yank. This may have been a little more difficult because of the prior use, but a pair of pliers wrapped in a towel should work on newer mufflers.
Once I removed the core, I noticed that about 1/3 of the original packing was pretty well scorched and disintegrated. I unwrapped the fiberglass portion to reveal a small segment of stainless "steel wool" which was also scorched, but usable.
My local Ace Hardware had stove door rope (for wood burning and pellet stoves) which is high temperature, and pretty dense. These come in 7' lengths, so I bought two packages. I tied the ends of the rope to the first and last rows of perforations, and wrapped the rope taut over the steel wool. Reinstall and ride. This should be closer to the standard core.
I also placed the original fiberglass mat back over the rope.
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Don't forget, Butterfly is slammed 3", so most normal and commercially lowered 1300's might not suffer this problem. I am going to take the "curb feelers" to Fastenal or Tractor Supply to look for a half-dozen replacements to keep on hand. 
