I know this post was YEARS ago but I need to know what you did to get the helicopter out of your exhaust! Just bought a 14 F150 with Roush intake and exhaust (sounds amazing!) but about a week after I took delivery I started getting that ridiculous reverb noise. My head feels like it's going to explode! Definitely didn't notice it on the test drive, etc. It's deafening, and the dealer claims to not hear it, of course. Did you end up fixing it? What did you do?

 

Google J-pipe and this site, should take you to the posts that talk all about this stuff. Theres mathing involved but I did it on my G8, before the j pipes, we could barely hear anyone inside the car, after, we could have normal conversations.