The toilet in my moms house (approx 35 yrs old) would “burp” or “spit” when you flushed it – like a bubble coming back up – and it would splash the water. We thought it was a problem with the toilet, so installed a new one about a year ago. Seemed fine for a while, now the new one is also “burping” when you flush. The toilet is on the first floor and the drain pipe goes out to the septic tank under the basement floor (so there is plenty of vertical drop). Anyone ever seen this phenomenon?