ya this same popping in the exhaust is happened to my 360 i just got. my cousin thinks its back firing and behind the pipes on the ground is a big puddle of black crap! the exhaust coming out of one tube increases so much it actually blows ur hand away from it when it pops. He told me to replace the spark plugs, then if that doesnt work go to the wires then finally the rotor. I have just replaced the gaskets from the headers to the block, my cousin also said that the header has a small leak but shouldnt be making that much noise! what do u guys have to say about all this?