Does any one know a good way to tell if your cats are still good?, I thought I heard them rattling again (like as if they clumped up again and are rattling around inside the housing) but now that I took the exhaust down I cant seem to make them rattle, I did however fail emissions badly when I took my last test ( too much unburned gas in the exhaust). I do have a pretty modified engine, but I did pass 2 years ago when I first put on my current cats.