Any results from the handbrake test??
Difficult to diagnose from afar and obviously difficult for those that have been up close and personal with your problem.
These types of noises usually indicate something amiss in the installation/alignment of the various springs/levers/cams that are involved in brake operation. If you were a DIY type I would previously have suggested that you dismantle, inspect and re-assemble as the only way to solve. Listening ouside while someone operates sometimes gives a clue.
