Noise when braking and coming to a complete stop. on 2008 Mercury Mariner

There is a loud creaking sound coming from my back right brake. It doesn't make the sound all the time and I don't think it is the pads because it doesn't start until the last few rolls of the tire when stopping. Any suggestions on what to check?

Was your parking brake on?
no, I don't even know where my evergency brake is... lol never used it.