The toilet drain runs across the room from the toilet to the plumbing stack on a slight slope. Sometimes things accumulate in the pipe that do not flush away, particularly if the house has settled and the slope of the pipe has evened itself. The worst culprit is long human hair, usually from cleaning hair brushes and throwing the hair in the toilet, or discarded dental floss. These long fibrous materials can stick to the walls of the pipe where it joins the vent stack and hangs over the edge of the vertical stack. They do not block the toilet, but the last bit of water that comes lazily down the horizontal pipe slowly and noisily drips off the ends of the hair or floss into the stack pipe. If you can't live with the dripping, it will be necessary to clear the drain line to the plumbing stack. This usually requires removal of the toilet from the floor to gain access to the floor opening.