I haven't heard the hushpower on a Mustang, but I would have to bet that the outlaws are worse. I have them on my car, and have messed around with them to reduce the drone. I insulated the trunk and back seat area, and put wide band muffler clamps around the mufflers, both of which have helped reduce the drone. They sound great outside, but can have some drone inside. I have gotten mine down to a tolerable level. Thinking of adding the BOSS exhaust, curious to see what that will to, I am guessing I might have to switch mufflers, overall might get too loud outside, don't want the extra attention of local law enforcement. :nogrinner
2013 GT 6 spd, GT500 mufflers, BOSS quad exhaust, Roush CAI, Barton shifter & 2 post bracket
CS GT-40 Wheels, Hotchkis sway bars, upper and lower control arms, springs (1.1/1.6 drop) and adj panhard bar KONI yellow struts and shocks J&M caster/camber plates,
BMR Upper control arm mount and lower control arm brackets.