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As the Skystar2 card does not have any audio A/D converter, the audio noise is actually being picked up by your sound card, most likely interference from the Skystar2 card while it is operating. For example, if you have the analogue 4-pin audio cable connected between a CD/DVD drive and the motherboard and this cable is resting or very near on the Skystar2 card, this is one possible source.
To start with, open up your DVB application and mute the TV channel such that you just hear the noise. Then go into your volume controls and try toggling the mute on each channel to see if the noise goes away. From my experience, the Line-in port is often enabled by default by most soundcards and can easily pick up noise.
If the noise remains even with the master channel muted, then you’ll need to check the audio cabling inside your PC. For example, if you have a TV tuner (apart from the Skystar2), audio cable to any CD/DVD drive, etc. try temporarily removing it from the motherboard or soundcard and check again. Try also using a pair of headphones using the same port your (front) speakers plug in to see if the noise is present on them. This way you’ll know whether it is the speakers themselves that are somehow picking up interference from the satellite card.
If you are using a dedicated soundcard and this is located in the PCI slot next to the card, try moving the soundcard or the Skystar2 card apart by one or two spaces apart.
Finally as a last resort, if you’re using the motherboard’s on-board sound, it may be worth getting a dedicated sound card, such as an entry level SoundBlaster. The vast majority of these will also have higher quality components and better A/D converters than the motherboard’s on-board audio.