Mdesign exhaust. After doing many different exhaust configurations first hand, including different sized piping, configuration of piping, and different brands of mufflers/resonators I've learned a lot in regards to the EcoBoost exhaust system when it comes to sound.
If you're going to modify your stock exhaust I highly suggest leaving the OEM mufflers intact and untouched as they do a great job in preventing dreaded cabin drone. The best thing you can do to the OEM exhaust is a modification of the "X-pipe" mod:
1. Cut out the resonator and third cat as you would per the x-pipe mod
2. Insert a 2.25" dual to 3" single y-pipe right after the flanges for the beginning of the OEM cutback
3. Use a 3" in-out Vibrant Ultra-Highflow SS Resonator
4. Come back into another 3" single to 2.25" dual y-pipe to mate to the rest of the factory exhaust system.
So you are essentially doing the X-pipe mod though a different configuration of it which will create a unique sound and kill any rasp.
Here is an example below to show the y-pipe to the single resonator though it did not go back into the OEM configuration and it is custom all the way through
