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I think the loudness might be close with the Flowmasters being a little louder. They sound different so I'd go with whichever sound you like best. I have GTAs and am happy.
I have the flows and think they may actually be quieter at idle inside than the stockers, you can hear them better outside the car though and they sound good into the throttle too.
Location: PA to KY ('07) to IL ('09) to MS ('10) to FL ('11)
Posts: 16,182
RE: Flowmaster or GTA axle backs
I've heard the Flows are raspy on the S197. I have the GT's (FRPP Stingers) which are louder than the GTA's and I find them to be excellent. Despite the drone at 1500-2000 RPM.
I've got the FRPP GTAs. They are a little louder and deeper than the stock mufflers from outside the car, little difference from inside - not too loud.