HELP my HDTV System has noise and sudden pause

Help, guys, I've been struggling with this for a long time, and still can't get it solved.

The music play back (and movie audio) will have random (not always) electrical noise in there, it's very short, normallly 0.1-0.2 second. Also, it will pause (no sound at all) for 0.1-0.2 second, and keep on playing. It only happends with my HDTV-PC, but doesn't come up with my DVD player.

I use to have this problem with my old system, though it was the anmp, then though it was the PC, maybe the sound card?

After replaced everything, I am still haveing this problem, now I really have no idea what's going on, can someone please help to think what's the reason? Thanks.

Current system:
PC: Shuttle PC SG33G5M, Intel Q4 6600 CUP, 4GB ram, 500GB SATA Hard Dirve,
Realtek High-Definition Sound Card,
Connection: Optical digital (Toslink) to receiver.
Receiver: Onkyo Sr805
Power: Belkin PF30 PureAV power Conditioner

Old System:
PC: Dell Inspion 510,4GB Ram, 250 GB hard drive,
Sound card: X-Fi Music sound card.
Connection: Co-Axale to receiver
Receiver: Onkyo Sr-505