Some broken catalytic converter chunks were found in the original aftermarket exhaust's muffler, which accounted for the rattling noises we heard. This miniature MagnaFlow muffler is actually a resonator from one of its Mustang kits. We pulled the entire prior-aftermarket system and straight-piped the exhaust with this small muffler and it was surprisingly quiet until the throttle was mashed, which was a testament to MagnaFlow's design.
2001 Ford F150 - Project Sinatra Part III: A Matter Of Breathing