I believe they may be talking about the common complaint once you get into the 40+k miles. A lot of peoples supercharger will make a rattling sound, mine did too. That might be what they fixed in the 5th generation. If not then heck any engine can be quieter. If its more than 1db it could be quieter, right? heh
Premium is what it'* designed to handle but it will retard a little, and change the mixture if it detects say 87 octane gas. You get better performance and milage out of premium, and your engine will prob last a lil longer.