As for the charging cord removal alarm, this can be turned on and off from the settings menu:2017 Volt . I have a 2013 Volt and the volume goes back to a lower setting after the car is shut off. Also, when the car has the charger attached, it sounds alarm if it is removed when the car is locked. I had my 2017 to the dealer and asked why the 2017 Volt wasn't like the 2013. They checked with Gm and were told that GM was working on the problem. It has been 6 months and still no fix.
from the Home menu - Settings -> Vehicle -> Energy -> Charge Cord Theft Alert (options On or Off)
As for the radio startup volume, there is supposedly a setting for this:
from the Home menu - Settings -> Radio -> Maximum Startup Volume. This brings up a bar where you can set a volume. However I've found it seems to be ineffective. Perhaps that is the problem the dealer is talking about.