Ive have a universal muffler with 2.5 pipe from the cat to the muffler. I have had it for about 6 months. It sounds great. Really loud!!! But recently when i let off on the gas, or barley tap on the gas, and every now and then in between 1-2 shift, the exhuast backfires or makes a poping noise. All this only happens at low speeds. It still sounds really loud and deep, but its embarrising when this happens. Do you think it is the muffer, welding, or the piping??? Any info would be great.