I have a general question regarding what other owners experience is regarding carbon soot build up in their exhaust pipes. I recently added a Magnaflow to my GXP and guess I notice it more in that the Magnaflow is shiny stainless both inside and outside. It seems that within a day or two the inside of the tips are completely coated with soot. Is this normal? It wipes off easily, just kind of bugs me! Any comments would be appreciated

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2007 Deep Blue GXP
All the usual dealer stuff
Painted GM Splash Guards
JPM Shifter,leather covered console,visors and door elbow pads
Fujita CAI and IC pipes
Kappasphere Re Bar,Little Chromies and GXP floormats
Magnaflow Exhaust
Mr Z Billet fluid caps
Nakid Stainless Turbo Cover
MBRP SS rear fascia insert
Slotted backup light covers
Stubby Antenna
Jay's Windscreen
Clear Bra
Custom engine cover
Painted Calipers with GXP logo and Red Arrowheads on center caps