This has occurred ever since ive had my beloved 172. Whenever ive stomped on the brakes quite hard, and let off, its like a pump is sucking the brake fluid or something? Makes a noise like this: "dzzzzzz" (say it out loud and youll get the idea).
p.s. for my new job i have to drive along some amazing back roads! it really does handle exceptionally well! could do with some new tyres tho!!!!