This happened to me last week, I have a 2015 2500 diesel, my truck had been sitting for two weeks, I started it and drove it only two minutes then rolled down the windows and listened to the radio. After 1+ hours the radio went to max, I turned it down and within 5 minutes it did it again, at that point it wouldn't turn down any more so I just shut it off. An hour later when I went to start the truck it turned over slow like the batteries were drained. I had the batteries and alternator check out and all were good. So I think in my case, the radio going to max volume is an indicator telling you the batteries are starting to drain to low. I did drive the truck for several miles after this happened to charge the batteries back up and the radio has worked fine ever since.
