This problem is well documented at Creative. They say that some graphic cards, mostly the new and good ones, have drivers that mess up the sound.
Their solution is to lower the hardware acceleration for the soundcard and graphics card. And then stating it is due to incompatible drivers from the graphic card manufacturer. Personally I think this is bull, but that seems to be the only thing that really works.
Hop on over to their site and use the solution finder under support and see for yourself.