Running the latest version of CS6 (current on all updates) on a Mac Mini i7 2.3GHz with 16GB RAM running OS X 10.8.2.
Whenever CPU usage starts to get a little heavy, sound will go silent at random times during playback of timeline in the program monitor. Meters go to zero when sound goes out and go active when sound returns. Video playback is fine and there are no dropped frames. This also was happening on my previous machine, a 2008 Mac Pro. Started happening with CS6 and never happened in CS5.5.
All my source footage is h264 from a Canon 5D. Sequence was created by doing the 'create sequence from clip' command. Program monitor resolution is set at 1/4. Played with setting audio hardware buffersizes to different values but with no change in behavior.