Despite the convenience of toilets in the average home, they aren't without their fair share of problems. One such issue is a gurgling noise coming from the toilet once it has been flushed, which is a sign that the toilet's vent pipe is partially clogged. The more persistent the gurgle, the worse the clogging is becoming, and steps must be taken to unclog the pipe or you're risking a backup.
Stand on your roof near the vent pipe and tie nylon cording securely to the end of a water-resistant handheld flashlight. Slowly lower the flashlight down into the vent pipe to see how far down the clog may be; if you can see the clog or the flashlight stops after a short drop, the offending obstruction may be close enough to the surface to remove.
Insert a yardstick down into the pipe to see if you can dislodge the clog. If the pipe is partially clogged, for instance by fallen leaves that have collected in the pipe after rain, then jamming the stick down into the pipe may help the clog move to the side and be able to be scraped away.
Slide the end of a garden hose down into the vent pipe if you can't see or immediately locate the clog. Turn the water on full to try to use water pressure to blast the clog from where it is stuck. This method also may help by adding water weight on top of the clog and force it to dislodge. Have someone stand inside the house in the bathroom with the gurgling toilet to watch for the clog (or leaks) to emerge in the bowl.
Use a plumbing snake down into the top of the vent pipe for clogs that you suspect are very deep in the pipe. Twist the line on the snake, which acts like a corkscrew and will "grab" the clog. Pull the snake out and repeat to remove the clog.
Contact a plumber if the above methods aren't successful. A knowledgeable plumber with experience should be able to ascertain the problem. Although this may be a little expensive, doing so will save you money in the long run.