MSI Laptop: Sound problems

[PeedeeS]

Ever since completely removing the pre-installed Vista from my MSI VR602 laptop and replacing it with Windows Home Premium, I get scratchy noises while playing a CD or DVD. This happens on the internal as well as external speakers and/or headphones. The troubleshooting tool shows nothing out of the ordinary. I have disabled all enhancements and have tried every possible setting. Testing the sound under the settings 16 bit, 44100 Hz (CD Quality) and/or 16 bit, 48000Hz (DVD Quality), gives the best results, although the scratchy sound at irregular intervals remains. Please help!