Brake Question 91 300E

[albions seed]

My wife's 1991 300E has developed a noise in the rear driver side brake. It is a squeak or squealing sound. The rotors and pads are relatively new, maybe 5k miles on them and still look very good. I pulled the wheel and cleaned and lubed the pad sliders thinking that they might be hanging up. Problem solved for about five days, the noise came back.

If you back up and apply the brakes the noise will go away for a while. That is until you hit a bump or take a hard turn. Any ideas????

Thanks