Where exactly are your mufflers and crossover placed in the system? This has a great effect on the audible resonations "drone" in your car. Like a musical wind instrument, the tuning of the exhaust note is much more complex than most realize. Position of the mufflers/resonators is critical to changing the tone/sound and the frequencies it resonates at. Moving the mufflers or crossover forward or back by as little as 6 inches can reduce or eliminate a drone at a certain mph/rpm. Try putting some large case hemi turbo mufflers on it and/or moving your mufflers/ or crossover if you have room. If those hemi mufflers don't eliminate or reduce your drone, no performance mufflers are likely to.