What's backfiring from our stock exhaust? How does it happen? What happen if we change the exhaust, is it still there?

 

Thats when you hear the exhaust "fart" or make a "popping" sound as apparent with rice rockets which remove thier catalytic converters. I have never heard anything about it exisiting with stock exhausts, but it may....but if it does its probably not too loud unless you've got a leaking muffler.

It occurs when reving high (either by shifting or just reving), letting go of the accelerator, then listening to the car make the fart/pop as the rpms come back down. As far as scientific details of how it really happens, I'm not too sure but it could be the exhaust is going the wrong way for a split second and the pop is the fumes burning up real quick.

 

Its unburned fuel. When you let off the accelerator, the butterfly closes and you dont get as much air coming in but since the momentum of your car keeps the engine up in the revs, fuel is still being fed but it isn't burned as effeciently. Hope that is clear enough.