Weird Noise?

Hey guys, I have this problem where when I drive around 20-35MPH and when there are small bumps on the road...there's some weird noises coming from what i think is the rear right wheel? what it sounds like someone with err.. "flatuant"... a deep one that is. haha. Could it be the brakes? I looked at the wheel and there's no nails in it whatsoever.