At the Sonic CD title screen while "Press Start" is blinking, press Down(3), Left, Right, X to display the sound test menu. Set one of the following sound combinations and press Start to activate the corresponding cheat function:

Sounds Result
PM11, DA09 View hidden scene
PM04, DA21 View hidden scene
PM07, DA07 View hidden scene
PM12, DA25 View hidden scene
PM12, DA11 View hidden scene
PM03, DA01 View hidden scene