Originally Posted by JB1

I have read through the thread but have not seen the answer to the question: what does cause the burble and gurgle? So I'll take a stab: As far as I know, the flames are unburned fuel getting into the exhaust and igniting/burning in the exhaust instead, resulting in popping/burbling noises. This is more present with high powered turbo engines due to running rich and the fact that the turbine housing and wheel get nice and hot and help to ignite the unburnt fuel.

This is all AFAIK, please correct me if I'm wrong...