Sometimes when I flush the toilet on the second floor of my home, the shower drain in the same bathroom makes noise. It sounds like the water is coming up the shower pipe and then draining down. Is it a clog in the vent or the wast line? Thanks..
Sounds like a partial clog in the main drain line.
You can try snaking the main drain line with a heavy-duty plumber's snake down the vent stack pipe on the roof or a clean-out plug, if necessary. Flush it down with a water hose sprayer.