A newbie so bare with me.. I bought an 06 that has had the AWE exhaust installed. I cant imagine this car without it! Sound is amazing except-

When at idle, there seems to be back pressure and causes an annoying puttering sound. When I start to move (1st gear) the noise begins to sound like an exhaust leak. Soon as you get rolling, the puttering goes away and all sounds normal. I have check for leaks and feel confidant there are none.
Is this normal? or should I have AWE look at it?
Thx

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2006CS Nav-Sports-AWE Exhaust-EVO Intake-Short Shifter-19" Cararra's-De Snorked..and of course Black on Black!