Soundcard problem? S7211

Hi, I am Tan from Malaysia.
I have bought my S7211 on February this year.
I have been using it without any problem except with a little problem, that is the sound produced is somehow bit distorted. The problem persisted even when I use a headset (altec-lansing).
However, I have found myself the solution by downloading the audio driver for my laptop from Fujitsu's website.
Even though some time after the problem still occurred, but it can be resolved by reinstalling the audio driver.
Until recently, I find the same problem came back. The sound randomly becomes distorted. In addition, when the load of the CPU increases suddenly, the frequency of the sound will change. For instance, when I am playing a song using Winamp and open 'Computer' from the Start Menu. Another example is when I played songs and scrolled the browser page. One more example is when I am playing a rmvb file using Media Player Classic. The change in frequency just happen so randomly.
I don't find myself able to solve the problem when I tried to reinstall the driver.
I am thinking to reflect my problem to Fujitsu's support center. However, before that I would like to post my problem here to seek some advices on how to resolve my problem.
Is it the soundcard problem? under Fujitsu's warranty?