I have a 2014 cts standard 2.0T.

About 3 days ago (not sure when it started as it is not audible with the windows up) i had my window down and was exiting my office building and heard a scraping scratching sound. my first thought is that it was the caliper of rotor and something stuck to it.

After driving home and driving myself crazy I have realized that it only happens when i'm coasting. Under acceleration or braking the noise is eliminated (or at least quieted to the point where I cannot hear it).

About 2 weeks ago i did replace the wheels with 19" wheels and run flats (vs the 17" wheels and run flats) but I did not hear this sound until recently.

I am heading to the dealership this afternoon....anyone have any thoughts? All i could find was a similar description on a GM truck website where they mentioned the driveshaft bolts coming dislodged from the rear differential.

Hope it isnt that.