Harmonic pulsation / Vibration?????????

This is the link I should have posted:
http://www.4secondsflat.com/SpinTech.html

"Traditional muffler designs remove sound in two ways: friction and absorption. Friction mufflers (stock type, turbo type, chambered) have high back pressure and can cause extreme high resonance and noise inside the vehicle at certain engine speeds (2000 to 3000) RPM."


"Our XL Sportsman series will give you the ultimate sound without the obnoxious drone of the competitions Tin Performance Mufflers."