I currently have a 2004 V6 3.9L Automatic / Single Exhaust Mustang. Im looking to get a little more rumble and muscle sound out of her... yet i didnt want to get a whole new exhaust system installed.

It was suggested to me that adding a new muffler such as a flowmaster or magnaflow would improve the sound to what im looking for as well has add a few more HP. Is this true?

I know with the year and style of my car i wont get a true GT sounding beast... but im just looking for a little more rumble than it sounds stock.