Well I have a 03 6.0 and when I got it I put a 4inchcat back system on it straight pipe.Loud as heck sounded nice.then got a sct tuner and put a 6 inch single stack on was just as loud if not louder.well I sold that stack and put on my 4 inch again and its quite as hell lots of whistle but the exhaust note is very quite.just wondering if it has something todo with it having to relearn the back pressure in the exhaust or what?.and its still straight piped.dumb questin but its got my confused

 

Tht is confusing. Mayb u were used to loud stack!