05 rendezvous grinding noise

i just got this car a week ago and after putting the car in park, whether i'm backing up or pulling forward it makes a grinding noise almost like brake pads rubbing (checked not that) sometimes it does it backing up and other times it does it after i have backed up and put it in drive just as taking off. was wondering if anyone has any idea on this because the service department cant seem to figure it out. any help would be greatly appreciated.

Most of the brake pads nowe are made of a semi-metallic composition. With that comes a higher degree of friction and better stopping power. But in addition, also comes the warm up time and the perpetual noise and grinding sensation it creates before they warm up. Many cars now will have that noise for the first few minutes of driving. There is nothing wrong and nothing you can do about it. Simply ignore it for 3-5 minutes and enjoy your new vehicle. (PS...I have a new Mercedes SL that does that...what a pain)