The hiss perfectly normal. Kind of a signature sound with these motors when you put a free flowing aftermarket exhaust with a true x pipe in it. Between 2000-2500 with the gas pedal released is where I get most of my hiss. Mine was not quite that loud with just the cat back but when I put on the headers it got much louder than yours.
As for the rattle it sounds like it could be the heat shield thats above the mufflers. There are directions with the exhaust that say to cut a portion of it off so that it will clear the mufflers, so if the shop didnt do that, that might be your issue. If they did remove it cut it and reinstall it it may be slightly bent from handling causing it to rattle, or not tightened properly. I dont know just throwing a few things out there.
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 STILLEN G3 / F.I. TDX (NO RESONATORS) / F.I. LTH / UpRev Tuned / BC-Racing ER Coilovers / DIY Oil Cooler / Short Shifter
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