: I have the same problem in my home. My upstairs masterbath washes through a wall in the kitchen. It's kinda gross, especially when you have company over, so I usually avoid using that toilet when we have guests over!

: If anyone has a solution, I would like to hear about it too.John Scates

For quiet pipes, the upgrade to no-hub cast iron is the way to go. Almost silent.
Many plumbers with use shielded couplings between the plastic vent pipes and the cast iron waste pipes. This is a bit more money, but saves the ears from unpleasant sounds. Terry Love