I installed the latest version of TMT3 about 1 month ago, so it’s not really old.
It seems to happen when a switch occurs, like when jumping from disc menu to movie. Maybe it’s switching from 2.0 to 5.1 audio, or something like that.
It was working correctly with my onboard sound card. I’m now using the ATI HDMI audio.
I’ve seen the problem with the movie The Warlords.