Do a search, most like x with straight thrus and H with flowmaster type muffs. The x and flows tend to sound raspy to most or some have said like marbles in a can at low speed.
flows and any off-road pipe is going to sound raspy...i had off-road mac h and flows (flows came on the car) before i got my borla catback...lets just say the borla sounds WAAAAAAY better...