I purchased the Xonar DG a few weeks ago. I get a loud hiss/buzz sound whenever I start to play any media. This noise ONLY occurs when I play a media file. If I am not playing anything there is no noise, and all is fine. For example, I click on a random Youtube video and then pause it real quick and I can hear the annoying hiss/buzz for a few seconds, and then it goes away..but if I continue to play the media, it will return and stay for the duration.
I've tried re-seating the card. I've tried inserting it into another PCI Slot. Nothing seems to fix the issue.
Think its normal. Windows tends to keep the audio output open for a few seconds after the last audio signal gets sent through, so if there is a brief pause in playback the audio output ports don't rapidly turn on/off, which in theory could damage the relays if it happens enough. My Xense does the same thing, as does my Realtek onboard chipset, and my G35 from logitech.
I've never had this issue with my onboard realtek. If I have something playing softly in the background, I can hear the hiss noise over the media..it tends to get annoying at times. However, if I have a song or whatever else playing loudly, then I cannot hear it.