Have you had your septic tank cleaned? Over time they do fill up with solids that can't be broken down.
+
Basically, the bubbling is caused by air in the line needing a pathway when you've sent water down. Your building vent might be clogged. you may need to run a snake down from the roof.
+
+
Also have you had your septic tank cleaned? Over time they do fill up with solids that can't be broken down. In addition the leach field may need repairs as over time plants can clog the lines. Bubbling can also be caused when the water is not able to drain into the tank.