I would check for leaks too, the combo is noticebly louder than stock however if is too loud its gotta be an exhaust leak. Since your going to be going under the car to check I'd recommend installing an O2 extender on the second O2 socket on the downpipe so you don't throw a CEL. Mine took a few weeks to throw a CEL from being catless without the O2 extender but then it started throwing one every week, i installed one earlier this week and so far so good, plus it was easy and cheap.
