Minor update: Got the GM customer survey to fill out online and indicated the FM Radio issue (among other things). I got a call back the next day and went over my answers and they gave me an opportunity to further describe the issue. She extended 1 year of OnStar to make up for my dissatisfaction, but I don't recall her specifically stating they were going to share my feedback with the appropriate department; though I assume they will.
I'm still awaiting my first oil change to bring it to their attention. I did try removing and re-installing the antenna mast, and noticed while secure (with thread locker), it wasn't fully seated. I screwed it completely down, and accomplished nothing measurable in my brief test ride, aside from messing up the black paint on the base of the antenna.