brake pedal pushes back when backing up

[psywzrd]

Have any of you guys been backing out of your driveway, a parking spot, etc. with your foot on the break and had the break pedal kind of push back at you? I don't know if I'm describing it the right way but it's almost like the break pedal grinds. Again, this only happens in reverse. Is this normal? It seems to only happen when I get to end of my driveway (which has a very slight downslope) and I'm ready to put the car back in drive.