Flows are quiet :not nice: and have been prooven to leech HP in some applications.
The loudest will be Magnapacks and SLP loudmouths. I think SLP is a bit louder though. Trust me on this, SLP do not use mufflers, they have resonators which amplify the soud. It DOES NOT sound raspy on a stock H, it can sound a lil bit raspy with the SLP X pipe.
The SLP xpipe comes in pieces so you can configure it, even choose to put on or take off the cats.
Now this is for the 04's and below, wait for them to come out for the 05's I bet they roar