I assuming you are talking about gurgling noise from the toilets, water bubbling when flushed? If this is the case there are a couple more of Q&A below this one. There might be a missing plumbing vent stack – go outside the house and look at the roof surface in an area above the bathrooms. There should be a 3” – 4” vent pipe visible above the roof surface. If it’s there it might be clogged with some debris, nests, dead birds, rodents, etc.
If all of the above seems to be OK, the plumbing vent system might not be properly designed, partially missing, drain line could be partially clogged, if you have a septic tank it could be responsible for such noises as well.
You might need a plumber to start going after all those possibilities…