Whistling speaker, sound card

I'm using Ubuntu 10.10. My sound card is Realtek ALC889A on Gigabyte-H57M-USB3. I bought a new 1+1 speaker (Mikado MD-208), but it started whistling and hissing. I thought that the speakers are broken; but I tried speakers on another computer and on a phone, there wasn't any problem with them. I think it is about my sound card. It is coming when the any sound application isn't playing on the computer, and when I play audio, the sounds goes. And there is an interesting thing about this, it is affected from computers processes (transferring data, moving mouse etc.) My headphones hasn't any problem about this. Thank you for all help.

this is 'sudo lspci -vnn' output
{{
00:1b.0 Audio device [0403]: Intel Corporation 5 Series/3400 Series Chipset High Definition Audio [8086:3b56] (rev 06)
 Subsystem: Giga-byte Technology Device [1458:a002]
 Flags: bus master, fast devsel, latency 0, IRQ 49
 Memory at fbff8000 (64-bit, non-prefetchable) [size=16K]
 Capabilities: [50] Power Management version 2
 Capabilities: [60] MSI: Enable+ Count=1/1 Maskable- 64bit+
 Capabilities: [70] Express Root Complex Integrated Endpoint, MSI 00
 Capabilities: [100] Virtual Channel
 Capabilities: [130] Root Complex Link
 Kernel driver in use: HDA Intel
 Kernel modules: snd-hda-intel

01:00.1 Audio device [0403]: ATI Technologies Inc RV710/730 [1002:aa38]
 Subsystem: PC Partner Limited R700 Audio Device [Radeon HD 4000 Series] [174b:aa38]
 Flags: bus master, fast devsel, latency 0, IRQ 50
 Memory at fbcfc000 (64-bit, non-prefetchable) [size=16K]
 Capabilities: [50] Power Management version 3
 Capabilities: [58] Express Legacy Endpoint, MSI 00
 Capabilities: [a0] MSI: Enable+ Count=1/1 Maskable- 64bit+
 Capabilities: [100] Vendor Specific Information: ID=0001 Rev=1 Len=010 <?>
 Kernel driver in use: HDA Intel
 Kernel modules: snd-hda-intel

04:02.0 Multimedia controller [0480]: Philips Semiconductors SAA7131/SAA7133/SAA7135 Video Broadcast Decoder [1131:7133] (rev d1)
 Subsystem: Avermedia Technologies Inc Device [1461:f31d]
 Flags: bus master, medium devsel, latency 32, IRQ 18
 Memory at fbbff000 (32-bit, non-prefetchable) [size=2K]
 Capabilities: [40] Power Management version 2
 Kernel driver in use: saa7134
 Kernel modules: saa7134
}}