The toilet is in the basement of a 2 story house right near the plumbing stack. I think this occurs when a lot of water comes down through the drain but I’m not sure. If you look at the toilet bowl. You see the water rise and fall and then see air bubbles coming from where the water runs out of the bowl.
We’ve cleaned the main drain a few weeks ago so hopefully not that but you never know.
One thing that’s changed recently is we had the shingles done. The roofers added an extension to the stack to raise it a couple of feet higher than the roof. This is intended to help with ice dams that happen right at that spot.
Thanks in advance for your expert advice.