[jb92563]

I think those pops and burbles are the open exhaust valve, unburnt fuel and compression waves exploding in the first foot of exhaust pipe.

In the Boxster I'd say its contained to the cylinder/exhaust manifold since that occurring in the header cats would shorten the cat life considerably and we would be throwing codes for rich mixtures.

F1 racers are notorious for that to the extreme and frequently have flame exiting the exhaust pipe because of the short distance for the unburnt fuel to travel and then igniting.