Loud and louder might describe SLP's (www.slponline.com) '11 Mustang GT mufflers. Two versions debuted at SEMA, both in stainless steel and with 4-inch polished tips. The more standard PowerFlo axle back retails for $599.95, the Loud Mouth is $439.95. More under the radar was SLP's (www.slponline.com) rear blackout panel for all '11 Mustangs. It's an ABS plastic part that requires no drilling or cutting. It retails at $59.95.