I have a similar gruggling noise in the shower drain, but everything is draining well. We have a home septic system which has recently been emptied and the pump serviced. Since then I frequently smell sewer odor, have gruggling noises and notice the water in the toilets moving.
Any ideas if the issues are related and what they may be due to?

This is a vent problem. Snake the roof vent. Good luck, Tom