I'm a pretty good home plumber but I'm not sure what's happening here.
Wife's bathroom, (I'm not allowed in there) :-))) This just started recently she says.
You flush and it burps. Sort of like it pops some water up instead of flowing around the and then down.
And...water slowly lessens in the bowl over a few hours. Underneath in the basement, no leaks.
It flushes well, just that sort of burp/pop when the water is released into the bowl from the tank.
It has a clean, no bends vent to the roof.
Now we have had some very hot weather and ac been running, but don't think that could evaporate much water from bowl...especially as much as it gets used.
Any suggestions?