I searched through the posts and found many about disabling the login sound, but I actually want to enable it. The problem is, it isn't working for me on auto login. When I startup the computer, after auto login, the sound doesn't play. But, If I then logout and and log back in, the sound plays, so it is enabled and working, just not on auto login.
I am using Mint 13 with Gnome.
I figured out that replacing the defualt gnome startup sound command solved the problem.
I went to the Startup Preferences and edited the GNOME Login Sound startup command to simply "play <path to file>"