Are you talking about air coming out of your vagina? The walls of the vagina touch each other unless something holds them open. If air gets into the vagina, and the walls of the vagina close together again, that air can come out all in one puff that sounds like passing gas.
It often happens when people are doings things such as moving around a lot, changing positions a lot, switching from vaginal sex to manual and back again, etc. because then air has an opportunity to get in, vagina walls close, air has an opportunity to get in, vagina walls close, over and over, every time you switch things up.