Hi all ...
Strange question but here goes...
I have a 2001 bugeye wrx and 3" turbo back exhaust with pop and bang mapped into the ecu .
Now I have a 3" open bell mouth decat straight through exhaust...when I blip the throttle when cold it sounds like it pops in the down pipe and not out the back box .... It's weird. Td04 by the way

 

It's not weird Most of my pops and bangs sound like they come from the down pipe or where it joins the center section. You need the right mix of oxygen and the right temp to get the unburned fuel to ignite in the exhaust. The conditions in that piece of pipe are obviously just right. The downpipe is obviously going to be far hotter then the back box.

 

Thanks for the reply buddy....