About 30 miles ago (5 days ago) I had my rear brake pads replaced and the Subaru dealer(05 Legacy GT) machined the rear rotors with some sort of machine that I could see attached to it.
When I stop harder now I hear a wu-wu-wu noise that was never present before they were done. I noticed the rotor is blackish in color instead of the normal shiny silver color like the front.
How long do I wait for the the new pads and machined rotors to seat/wear down?
This sounds to me as though the new pads and turned rotors were NOT mated on completion of the work. The blackish color is likely brake dust.
Thanks for response but what does that mean? Wait a while for mating to occur or go back?
You can mate the rotors and pads yourself.
Drive down the road and when there’s no traffic behind you, apply the brakes firmly. Do not hammer them on, just apply firmly. Do this three or four times.
If they still make a noise take it back and take the tech with you and let him/her listen for themselves.
Usually a tech will test drive the vehicle and mate the pads/rotors to prevent a squealing noise that tend to come from ceramic type pads.