I looked under my car the other day, and noticed that there is either 2 or 3 cats, and 2 mufflers. I was wondering why it has so much stuff in the exhaust?

 

isn't that the whole cat-back system? should be the y-pipe, b-pipe and stuff...

 

What you are seeing is true. There are precats on the original y-pipe, plus the main cat between the downpipe and b-pipe. The second muffler you see is the resonator. Basically your exhaust needs to breath, its choking lol. You need to get an aftermarket downpipe, randon tech convertor, and a muffler. When you get all of that go to a muffler shop and have them weld you a catback(BPIPE). I realize that all the catbacks for the maxima comes with a resonator, thats not needed in my opinion. Hopes this helps, if you do decide to get a muffler i would recommend either the HKS Hyper muffler or the Apexi N1 muffler.