well first of course, if you are worried I would encourage you to consult a fully qualified doctor. I am not yet qualified, and hence I cannot give you formal medical advice.
As a general observation however I would observe that your bladder is right in front of your vagina - and thus as you tense your detrusor muscle to void, you will also squeeze your vaginal canal - and hence any air pocket in there will be be expelled. Indeed I have experienced this myself, and I know some natal women also do.
Now as I explained I'm not yet qualified to tell you whether or not this is what is happening with you, nor indeed could I do so with any certainty without examining you and taking more details, but it sounds to me at this stage as though this may be a possible cause. So I repeat, if you are worried, go see your physician, which all anyone not medically qualified can (or indeed should) tell you.