that's just going to add confusion for the judge/jury... Just tell them that you have a 100% street legal aftermarket exhaust as your only modification. Then tell them that you did not hear your car backfire and this is the first time you've ever been told that the car has backfired. Tell him that you have since done some minor maintenance (changed spark plugs and O2 sensors) even as a precaution against any further possible backfires even though you doubt your car ever backfired before. It'll get dismissed Im sure.