cats need cutting?

Is there any given way to tell if your cats are stopping up? Mine make this horrible (very loud) popping noise after the truck has been running for a few miles, and it does it for ever after I cut the truck off, so I know one of them is getting pretty hot...???

mine used to do the same thing untill i put my catback system on and it stopped.i thought it was the muffler or heat sheild on mine making the noise