Bad/clogged catalytic converter?

Have a 99 Ram 1500 , i started it the other morning it was chilly (13,14 F) when the truck started i noticed there was a change in the sound of the exhaust, now i have a Flow-master 40 series muffler with dual pipes but i noticed something wrong , (not because it was cold) it was more throaty and when i reved it i just sounded different , hard to explain, the noise didn't go away once the truck was fully warmed up and it is at and idle and while driving it does this, crawled under the truck and the sound gets louder from middle rear to the rear end of the truck, any suggestions would be greatly appreciated the truck has about 100800k Mile. Thank you