Snostuff Rumble Pack S-D Xp 800 E-Tec S 331-413 If you are looking for performance, you have come to the right place. Sno-Stuff Rumble Pack Silencers continue to set new standards in the industry. All Rumble Packs are designed from the ground up with performance, quality, and reliability as primary goals. Extensive dyno testing with the best equipment available insures accuracy and honesty that others can not match. Depending on the application, you can expect up to a 5 hp gain and a 9 lb. weight loss.