When applying brakes and the car is about stopped I hear a whooshing sound?

When applying brakes and the car is about stopped I hear a swooshing sound like fluid is bypassing something, the pedal goes down farther and the car moves forward like a loss of brakes, then it does stop as the pedal goes farther down. The noise seems to be coming from the master cylinder area. My question is there a test to see if the master cylinder is bypassing a plunger, and, or why does it just do it as the car about stopped. Have new pads, rotors, calipers, no leaks anywhere.I just hope its not the ABS, I hear its quite expensive.
Thanks