air filter...no but seriously....terrible idea. a borla sytem i once saw used a few different plates with different sized holes to control exhaust sound by bolting it between the tail pipe and exhaust pipe (the muffler section branched off). perhaps, if you really must quiet the exhaust down with the worst way possible.....drill some fucking holes in the plate you welded into the tube....try a 1 inch hole in each tube holy god man why would you do that