I had a Cattman exhaust system put on about a month ago (resonator on back) and I am hearing a banging/rattle over bumps. I'm hoping it may just be an extra hanger or support needed than what was provided. Any other org.ers with this problem. It actually sounds like part of the pipe is banging against the floor of the car.
My wife thinks it's still too loud and won't drive the Maxima so I can wheel around in our new FX

 

I'm thinking its either the b-pipe bumping against the cross brace... or the rear section piping knocking in that little "tunnel" through the suspension... either way, it should be easily solvable. Some people just remove the cross brace if that's the cause (just take it off and drive around for a bit to see if it persists), and if its the other tunnel problem, see if you can jam something in there, like a spare rubber exhaust hanger or something....

On my car, my (huge) GReddy muffler tip hits the bottom of the rear bumper when I go over bumps... but if ya say its coming from the floor, that can't be it....

If there are other possible causes, I'm sure someone else will comment.

 

Mine rattled slightly after I went to the strip. I figure the torque from launches caused it to move slightly. Mine was rattling against the heatshield around the muffler. I did some some adjustments to the hangers and got it to stop. I have the stock muffler with Cattman Y and B pipes. Some people suggest getting aftermarket hangers from NAPA or Autozone.

 

On the Cattman 9/10 times it's hitting the brace between the floor pans in the rear-it goes across the tunnel. You could wedge high-temp exhaust bushings, like the rubber they use on big rigs. Or you could just take it off, i don't believe it serves a structural purpose. My Greddy hits the bottom of my bumper too, it burned a nice cutout for itself. It actually looks almost stock. It used to hit ever-so-slightly above the rear suspension cross-brace like Puppetmaster said. But then again so did the stock NISSAN exhaust.............Japanese quality. In the end i got a new muff-hanger, the rubber part, for the right side of the muff, and it raised it a bit, and now it's actually better than when i bought the car. Good luck