Gurgling means air is moving through the drain system in an unusual way. A partial clog in the drain line is one possible cause; a blocked plumbing vent can also disturb airflow. Notice whether the sound occurs at one fixture or several, and whether water drains slowly or backs up elsewhere.
If multiple fixtures are affected, odors appear, or water backs up, stop using the affected fixtures and have the system checked. A plumber can locate the blockage or vent issue and recommend the right repair. Contact Stanley for plumbing service.