I've been getting a similar thing for months . . . ever since the Nurburgring, come to think of it (!) - no noise when actually braking, but when easing off and coming to a standstill there is definitely something going on there - noticeable vibration and noise ! I'm assuming its coming from the brakes, of course - could be totally wrong ! I'm expecting I probably need either new discs or pads . . but need a specialist to investigate !
S.