Heed the advice from the posts above!
I will add that the "popping" being too rich will not back up into the intake. That's false. If that happens, that is considered a "backfire". That can destroy an engine quickly and is indicative of other serious mechanical issues going on. That's not something that will happen from a cat-back exhaust mod. The exhaust popping is after-firing and is fairly normal due to the emissions controls and the fresh air injection into the exhaust to burn up the unspent fuel. It is corrected partially by blockoff plates and proper tuning. Over time, this behavior can damage the exhaust if it continues. It will degrade the silencer packing. Aside from those things, it's not going to hurt much else in the motor if it isn't back flowing into the engine itself. And that would require you to open the motor and inspect the pieces (valves, pistons, rings, etc).