just some useless information. i have an 06 5.4 scab and i had the muffler replaced with a straight pipe, it sounds good not like the sound u would think of with no muffler(actualy kinda quiet compared to a chevy or dodge WITH a performance muff). the flowmaster 40 series i put on didnt even make a sound change from stock so i took it off. now i have my exhaust cut off about 2 feet after my y pipe dumped under my truck. it does resonate inside a little bit but its tolerable and i like it better.