A common problem for many homeowners is a toilet that starts bubbling on its own. It might freak some people out, but it is not as serious of a problem as you might think. It is however, a problem that will need your attention. Most commonly, this is caused by a blockage in your plumbing system. If gas gets pushed out of the way by water running down the pipes, that gas will need to go somewhere else. Usually, it will go out the vent pipe, but if this pipe is blocked, your toilet is often the easiest exit.
To find out what the problem with your vent pipe is, you might need to go up on the roof. There you should be able to use a camera on a snake to see if there is a nest or some other type of blockage inside of the vent pipe. Removing this should solve your problem.