I've been through Super Turbo's, Ultra-Flow's,
Borla's, Magnaflows, Walker Quiet-Flows...they ALL DRONE, unless you're running longtubes. The only things that don't drone are Dynomax VT's, which I currently run, or run the mufflers of your choice that have the sound you like, and adding capped 1/4 wave cancellation pipes.
Video of Dynomax VT's on my mustang, with the microphone under the console directly below the armrest.
Decible readings before and after putting 1/4 wave tubes on my G8 GT, and the only reason I don't have them on my Mustang is I have no room for them with a catted H-pipe, torque arm, and
panhard bar. 1o dB difference means it's half as loud now as it was before in the drone zone, which no longer exists on this car.