l noises during ?

When I was having with my ex bf if we swap positions or after hes pulled out sometimes a farting noise happens, but its not from my bum...its really embarring & I just go bright red & pray he didn't hear. I got into the habit of just staying as I am till he goes in the bathroom & I hear a flush - then I move, so that the flush of the toilet is louder. He saw me get really embarred & self conscious once & said "don't worry its just because there's air inside you" which made me really relieved. But most boys haven't a clue about that, it happened once with my bf before him & he was laughing asking if I'd farted. People laugh & make jokes calling it "fanny farts" but I was just wondering if its normal & if anybody else gets it? Anybody brave enough to admit it would make me feel a lot better...thanks.