There is some sort of popping noice or rattle in my exhaust note

Any ideas what this might be ??

Does it run smoothly otherwise? When does it pop, on acceleration, deceleration, randomly, or what?

well popping and rattling are 2 different things which is it do you have a aftermarket exhaust? cause an aftermarket exhaust does cause the car to backfire if you run it to the point where the secondary injectors (3.8k)kick on then drops below it does back fire/pop but a rattle could be a loose heat shield on the cat or precat or its no fully hung anymore

I have had 5 or 6 different Rx-7s and I have always had a slight popping sound in the exhaust while the car is warming up.