I used to get the same thing in my old Volvo 340 years ago (and that was a 70hp 1.4)

When I asked my mechanic about it (guy was 64 had two hip replacements, and still was shifting engines around, including helping me turn a 1litre mini a-series engine into a 180hp lump) he mentioned it was something to do with the baffles popping. Don't know if that sound is similar to the one you're describing, but still it's a thought.

 

I think it just happens when you get a high flow cat/gut cat/remove cat...I built a 20/22r removed all emissions crap, removed cat, 2.5 " exhaust, 22r carb rejeted, the plugs run the perfect brown paper bag color although I do have the timing set so it wont ping with 89 octane so that is probably my problem. Sorry for a worthless post but I wanted to put my $0.02 in...

 

My 95 blazer makes the popcorn popping sound when accelerating and a little bit while idling. Could this be a bad cat? It seems to bee coming from that area

 

Sounds to me like you have low fuel pressure. Usually caused by a failing fuel pump and/or restricted fuel filter. I replaced fuel pump and filter on my 2000 Sierra due to low pressure. You need a fuel pressure gauge to check pressure at fuel rail. Gauge is not expensive and you can search web or other means to see what the fuel pressure for your vehicle should be.

About the "popping" question, as soon as I modified my exhaust, it popped upon decel. Installed shorty headers and two flowmaster race mufflers. No cats either......shhhhh! I do have some high flow cats on order though. Pops only when decel from highway speeds and only in certain rpm range. Can't think of it right off hand. Truck sounds like a beast. Wife doesn't care for it. Lol