Same thing happened to me. I uninstalled GTA, deleted all the left over files, reinstalled my soundcard drivers, restarted, reinstalled GTA, reinstalled MTA, and it worked. Definitely a bit overkill, but this is the only thing that did the trick for me. I think this problem has come up with a lot of people using Audigy cards, or the VIA onboard sound that comes on a bunch of Asus boards.