the noise you described might have something to do with the snorkel , that is if you never herd the noise be for you added the snorkel. ive herd a popping noise twice . first time i herd a noise like that was from abuddies rubicon after he wrecked it hard. it was the front end some were in the drive line was popping when he turned the wheels. but that wasnt hard to figure out cause the whole front end was completly trashed on the count of him running his 4wheeler of the end of a train trussel . the other time i herd popping was from my friends foreman when he was trying to make his own exhaust, and that was because he had to much back pressure from running to small exhaust , which resulted was major engine failure , threw the rod out the bottom of block and then some. maybe that snorkel is to restrictive cause n some kind of detonation issues , are you shur its a pop not a rod knocking?