Plumbing Questions? Ask a Plumbing Expert.
Hello, if the waste line from the toilet does not tee directly into the 4" house sewer main, but runs horizontally for more than 5 or 10 feet, there may be a vent pipe tee'd into that line that runs to the roof... if that is partially clogged you will have the problem you describe.
If the waste line from the toilet is within a few feet of the 4" house main sewer line. and there is no separate vent, it needs to be slopped 1/4" per foot toward the 4" main, if not that would contribute to such a problem... If the the line from the toilet has the proper slope, then there is likely some sort of blockage in the main sewer line that is backing water up to the toilet connection to slight degree. When that happens you would have the problem you mention.
The older the home the more likely the main sewer line is not not draining properly. If you can inspect it, and if it is cast iron pipe then the problem could be roots growing into the line through a lead / oakum joint, or a tree root growing under the sewer line raising it enough so that it does not drain well.
We can go from there if you need more discussion, without any time limit.