I got my Flowmaster installed a week ago. I picked up a 50 series model with the dual 2.25" inlets and single 3" out. This seems to have made a difference in how the engine makes power. With the supercharger the reduction in back-pressure seems to allow the boost to come up faster. I'm sure the exhaust note drowns out the whining so that may be the larger effect.
Generally I'm quite happy with the results. I've lost the Y-pipe and increased the volume which is what I was after. The 50 series has a nice note and is somewhat aggressive. I wouldn't want it any louder. Now I'm thinking headers and high-flow cats. Those will have to wait for the gauges and hellwig.