Turn on the PlayStation without a CD inside and access the CD player from the menu. Now insert the game CD and 2 tracks will be indicated on the screen. Choose to play track 2 and you will hear over 5 minutes of Mortal Kombat 3 sounds.
Secret Options
This secret menu is available in any of the games in Williams Arcade's Greatest Hits. Just pick a game and enter it. Once in the game, hold down L1 and L2 buttons and press Select and Start simultaneously. First, a game status screen will come up. Press X to skip to the options screen, where you can adjust the difficulty, number of lives, and other settings of the game. Once you're finished, hit Start to return to gameplay.