If it were music then I'd look up an application which can play music in the background without any windows or anything, and make a batch file to execute that in addition to any other stuff you wanna do, like the code on this post, of course then change the icon and name to something not suspicious. I know there's an easy way to code in a pretty much unstoppable shutdown timer including a message to display while counting down. If I recall correctly there are a lot of tutorials for that sort of stuff floating around the internet, including on youtube.