Thanks for clarifying the conditions under which the music appears.
Don’t know if the 2018 Volt Owners Manual is yet available, but the Infotainment section of the manual for the 2017 Volt says simply that the vehicle "has an infotainment system. See the infotainment manual." IOW, the infotainment system has its own manual. A quick internet search might provide you with a source for one. Some of your issues may be discussed in that manual.
Back in my day (2012 Volt) the two were an Owners Manual and a Navigation Manual (which covered the radio, phone, navigation, etc.). Later model years maintained an Owners Manual for the Volt for the given model year, but the Navigation manual is no longer specific to the Volt. It’s now the Chevrolet MyLink Infotainment System manual, covering the infotainment center found in several Chevrolet vehicles.
For example, the introduction to the "2017 Chevrolet MyLink Infotainment System" manual states, "the content may apply to the infotainment systems found in the Silverado, Colorado, Tahoe, Suburban, Camaro, Cruze, Malibu, Impala, and Volt vehicles... The information in this manual supplements the owner manual. This manual includes the latest information available at the time it was printed... This manual describes features that may or may not be on the vehicle because of optional equipment that was not purchased on the vehicle, model variants, country specifications, features/applications that may not be available in your region, or changes subsequent to the printing of this manual."