You said you used the Full TNT patch......
How is it configured?
The FF7config.exe program, I mean.
Are you using Software Render? Because if you are....there is no reason for installing the TNT patch.
Try changing your direct sound to Basic Acceleration.
Type dxdiag...to get to that menu. It's in the Sound Tab. Don't need to reboot for it to take effect.
I had a problem like the one your discribing once...on Win95...a very long time ago. It turned out to be a codec Conflict. At the time I had removed all the Video and Audio Codecs from my machine.....and it fixed it. But that was with Win95, I have no idea what the procedure would be with WinXP to remove the Codecs or if it would even fix anything...or break something.
With Win95 removing them, didn't uninstall them from my machine.... The OS would just reload them as it needed them, automaticly. I removed them thru Control Panel's Multimedia Icon.....on that last tab.... I had just selected them, and picked remove and then rebooted.