Can You explain is this:
The frontal tab suddenly push deep in my rectum and "Pop" like sound can be heared, a fart sound also. I feel Like something comes out from my rectum
Is it just air, lubricate or something else?
I'm afraid you're going to have to reach you own conclusions on this one. Might be too much lube, a reaction to something in the lube (glycerin for example might give you an urge to use the bathroom), air or water inside you from douching before you sessions, pushing during contractions or just normal ordinary farts or...
I'll just say that it should not worry you if you have a thick towel under you to catch any normal drips and drops from a session. I use large beach towels and they are reserved for sessions only and very worth it for how long they last and the peace of mind they give.