Recently my rear pads have begun to squeal after I first drive the car, after letting it sit overnight or for several hours. (when all is completely cold) Two or three stops the squeal will go away. I can live with it, but it drives the other half nuts.
With 176k miles on the clock, I recall changing the pads and rotors about 2 years ago.
I bought Zimmerman rotors and OEM pads.

Checking both today they are well within spec. I put some more grease on the back of the pads, but the squeal persists. I do notice some some darker areas on the rotors, that go completely around the disc but do not cover the entire surface from inside to outside. Just a narrow line about 1-1/2 inches wide. I feels a bit uneven, the surface, but are not warped. Should I have someone turn them smooth? Maybe change the pads again?
Your opinions are greatly appreciated.