exhaust drone/harmonic resonance

You need to run the pipes out the rear or at the very least, out hte sides. You have to get the sound out from under the car. Also, try adding a set of Dynomax bullets. I had a single 3" on my Bronco. After 2 hours, I was at the point of vomiting from the drone. It made my head hurt so bad, that I eneded up staying at a friends house just so I didnt have to drive. I added in a second bullet and the drone was about gone. Also, if you have an x-pipe, maybe swap it out with a 2 in 2 out style resonator. This is done on a lot of modified Tbirds that have the supercharged 6. Most prefer Borlas.