ES2K

Update 2-5-12: My front pads were worn; wear indicator was only making noise when I backed up. Did a brake job this weekend. Poterfield R4S pads. New OEM front rotors. Amsoil 600 fluid. All is well.
My '06 is making a groaning sound when I back up slowly (parking brake off). 43K miles. There is no such groaning sound when I am moving in a forward direction. The groaning noise sounds like it is coming from a brake. Is this a symptom of a sticking caliper? Anyone have a similar experience.
T

S2_4SHOOR

First, I would check inner and outer pads then go from there