Brakes making noise in reverse, not in drive.

For the past few days my brakes have been making "noise", like the pads are worn when applying the brakes in a reverse situation (backing down a driveway etc). The brakes will continue to make noise for one or two stops after this, even when in drive--but after that, there is no more noise. I had my brakes checked around 9 months ago and they had around 70% percent remaining f/r. I thought that maybe the wheel cylinders had started spouting and were contaminating the pads or shoes, but that isn't the case. It seems as if the pads are moving around a bit when applied in reverse, and they "bed in" again after one or two stops.
Does anyone have any insight?

Better pop those drums off and have a look inside...