To get sound test: On Title Screen, press Down, Down, Down, Left, Right, A Insert these numbers: 46, 12, 25 Then there is the message! It will play the Boss battle music.
Its not really an evil message, it just sounds like it. The real meaning is "Tanoshi sa (Fun by [from]) SEGA ENTERPRISES -- Madjin" (Source from TD9001)
If you have a video of showing the hidden Sonic CD message, leave a video response. (Automatically approved)