This may sound crazy, but it works on my Mercedes. I have the same problem with it once in a while. The guy that works on my Mercedes told me to put the car in reverse and get up a little speed and stop suddenly, I don't lock up the brakes but I apply them pretty hard. I do this 5 or 6 times and the problem goes away for several months. He said that it knocks the glaze off the pads that forms. Putting the pressure on the pads in the opposite direction is what fixes it he said. It does work for me. Give it a shot. It can't hurt. Warning...it does make me kind of car sick.

Does your Mercedes have the squeak even when your brakes are NOT applied?  Mine does it when I'm not braking and then it quits when I apply the brakes.  I will definitely give your fix a shot though.  I'm willing to try anything at this point. 

On my Mercedes you hear it when your starting out going slow. If you apply a small amount of brake pressure it stops.

That sounds pretty familiar.  I'm going to see if your fix will work. 

That method has merit, and often works.   You can also use a antisqueek product that goes on the friction surface of the pad, not the backing.  NAPA used to carry it.  It seems against every known good thing to put something on the pad surface, but it does work.   The first few stops seems like you are stepping into gravel, but after several stops they are quiet forevermore.   Do not use any other type product on the surface of the pad.    You could try some things on the backing as well.

I'll give that a shot.  Thanks!