I was just wondering exactly what is that machine gun, drum beat, rat tat tat tat tatt, noise that ocours before a backfire and flames? Is it smaller backfires occouring in the exaust or somehtign else? Not relaly important jus wondering. I tried to upload a vidoe that displayed this but it was too big.

 

its the warning shots for cars to back off before you spit unburnt gas all over them

 

^^^nice^^^

 

My best guest would be as you said small backfires occuring inside the exhaust. I would assume they are smaller due to lack of oxygen. When the unburned fuel leaves the exhaust and hits the oxygen...along with the heat coming with it you get a louder backfire. That is my best guess.