I dont know for sure what the flowmasters sound like so its hard for me to compare. But I can tell you how the ultra flows sound. Idle sound quality is nice and in no way overly loud (about the same as the super turbos I replaced). Just off idle and or at a low RPM load (25 mph in town in 3rd or 4th) the sound comes up and is very deep (this is the worst area for these mufflers as far as sound control). As the RPMs come up the sound goes down and smoothes out. With a full interior conversation is not a problem on say a highway drive and I am running 3.91 gears.
In short. At idle muscle car quiet, low RPM under load much louder, midrange RPM driving smooth and deep with a very acceptable sound level increasing slowly and progressively as the engine increases in RPM.
