2 or 3 large air bubbles almost like belches come up from one of our toilets without even flushing it about 8-9 times per day. It has been happening for about 7-8 months with no other problems in the home plumbing lines. The shower is the lowest point and it is not backing up. Their is no odor either. What do you think?
If you have septic tank it could be full are pipe partly stopped. If you are on main sewer then it is partly stopped when you use small amount of water it backs up slow, are you could have stopped up vents. Take a 5 gallon bucet of water and dump in bowl fast and see if it backs up, sounds like a cable job for somebody, let me know.