I'll try to explain the difference as best I can:
Backfiring through the carbs is rather loud by comparison and happens a lot closer to the seat/sidecover area. It is sometimes accompanied by an unpleasant smell (if the air cleaner element gets singed) and poor running.
The popping or burbling in the pipes are more closely associated with the sound your uncle makes breaking wind on a leather couch,
(more subdued, but still embarrassing) and usually only happens upon deceleration.
It's pretty easy to see if your AI system has been removed by looking for two silvery pipes right next to your spark plugs (just outboard of the plugs). They'll have rubber hoses connected to them which disappear up under the tank.
If you find only two little plugs there, your AI system has been removed. This is by no means a completely definitive answer as some folks disable it without removing the pipes by blocking the larger (unseen) hose up under the tank with a marble.
See if you can find some local RATS to friendly up with for better advice. Usually they'll be more than happy to provide guidance for the low price of a beer...
Good luck and keep us posted!