The sound a woman makes when a man "face fucks" her.
When a woman gives you a blow job grab the back of her head and forcefully thrust your cock in and out of her mouth as fast as you can. She will soon be gasping for air, as you continue to mouth fuck her she will sound like a duck quacking as she gasps for air.
When a person is "eating out" a female and spits into the vagina. The female queefs and the spit flies back into the person's face, making a sound similar to that of a goose.
Dude, don't date that chick, she goose quacked me.
Quacking is a term which refers to the loud guttural sound which reverberates from a females esophagus as a penis is thrust into it and then removed forcibly creating a suction-force induced sound which resembles the characteristic harsh sound uttered by a duck.
"Yo dude !! - I fucked that bitches throat so deep and hard last night she was quacking! :"GWACK GWACK GWACK GWACK!!!!!!!!"