Rear brakes make a thumping/thud sound...

[cigarpointe]

This is my first post on the board. Just got my 2SS L99 about 2 weeks ago. Love it, but sometimes I hear a thumping sound coming from the brakes in reverse or in drive. And I hear it when I'm moving slowly but applying the brakes. My drive way has a downward slope so I basically put it in drive then creep forward applying some brake pressure. But it also does it at random times, like when I'm at a stop light and creeping up slightly. And it's not all the time ever. I hope it's nothing major. Just weird to me. It sound's like a thumping or a thud sound. Anyone else experience this?