My Fast Intentions / Berk HFC setup had been getting severe drone (from 1500-3000 rpm). It was droning at almost all speeds except 70+ mph. I contacted Tony at FI and found out that my center Magnaflow X-pipe muffler had burned out all of the sound insulation. It was essentially an empty echo chamber that was amplifying exhaust drone. Unfortunately Magnaflow will not warranty these mufflers. Magnaflow also quietly redesigned the muffler. Tony built me a new center section with the new muffler design. I installed it today. Now the drone is all gone. For anyone with an older FI exhaust that drones, tap on the Magnaflow muffler. If it sounds empty, then you need a new muffler.

 

not sure about hfc, but with tp this will naturally happen to any and all sound supressing material in it's path. This is also why newly installed exhaust videos are completly useless. I use the same x-muffler on my invidia with test pipes, even after the fiber have burned out, i don't get any drone. So only time will tell how drone-free the new muffler will last.

Do you know what the redesigned was for the muffler?

 

The old Magnaflow design had the inlets and outlets toward the edges of the muffler endcaps. The new design has the inlets and outlets inset toward the center of the muffler endcaps.